Popular Science Monthly/Volume 13/September 1878/The Teredo and its Depredations II
By Dr. E. H. VON BAUMHAUER,
COMMISSIONER TO THE CENTENNIAL EXHIBITION FROM HOLLAND.
CONTRARY to the opinion of Sellius, who regarded the teredos as hermaphrodites, Quatrefages has taught us that they are of both sexes and that the ratio of males to females is about one to twenty. The females are oviparous. The eggs are expelled by the branchial siphon: Quatrefages found them in that siphon and in the branchial canal itself. The mode of fecundation is, however, unknown; it is supposed that, in that act, two different teredos project their siphons and bring them in contact.
As regards the metamorphoses which the eggs undergo, either in the branchial tubes or in the water, nothing has been added to what was made known through the researches of Quatrefages in 1849. That naturalist has taught us that the eggs pass through the series of modifications, from the starting-point, which one meets with in the examination of all animals—i. e., the formation of the germinative area and of the vesicle of Purkinje, the disappearance of this and the breaking up of the vitellus. The eggs undergo their development in the branchial cavity of the mother; the embryos resemble very small, rounded animalcula of vesicular form, and are provided with vibratile cilia, by the aid of which they have regular movements, and probably are expelled from the branchial cavity into the siphon. In a third phase of development the bivalve shell is formed, the foot appears on the outside, the vibratile cilia form a sort of crown, and the embryo thus possesses the faculty of locomotion as well by creeping as by swimming. The development of the eggs takes place from time to time, and especially in the month of June, although even as late as the 29th of July Harting found eggs in all the teredos which he opened. The development of the eggs progresses very rapidly; in four days they pass out of the embryonic state, fully equipped for living in wood. Toward the end of June, Kater observed them in large numbers on the surface of wood, and by the 15th of July he found them in the interior in the form of perfectly-developed teredos. Even in the month of December, but no later, he saw young teredos enter into pieces of wood placed by design in the water; at that time they were from eight to fourteen days old, and, although very small, they resembled in every respect older teredos.
Teredos penetrate wood naturally by very small openings in a direction perpendicular to the surface (Figs. 12 and 15, C); then they generally turn about in order to follow the direction of the woody fibres, Fig. 12.—Wood exposed from November, 1874, to September, 1876, in crib at Pier No. 1, New York, North River, twenty-five feet below mean low tide. usually upward, but sometimes downward. Although they do not enter into the earth or mud, one generally finds the first traces immediately above the line of the mud in which piles are driven; it is at this point that piles destroyed by the teredo generally break off.
When the teredos are lodged in a piece of wood, one recognizes them by very small holes on the surface, and the extremely delicate tubes which project from them (Fig. 12, e, d). These are the siphons, only one of which shows at first, the other appearing later. These siphons are generally kept outside the wood in the water, but the slightest touch causes the animal to retract them. One of them is shorter and larger than the other, but they both seem to serve for the expulsion of the fasces, which largely consist of particles of wood reduced to a very fine powder. It is known that the teredo does not perforate wood for nourishment, but only to procure a suitable abode; the woody substance, detached in the boring, passes through the intestinal canal, and then is expelled in the form of a very fine white substance by one of the siphons, generally, according to M. Vrolik, by the shorter, but sometimes by the longer. The long siphon appears to serve principally for the introduction of food, which consists of infusoria, diatoms, and other inferior animalcula, which the sea-water brings with it into the siphons. It is nevertheless still uncertain whether the matters expelled through the longer siphon come directly from the intestinal tube, or if they are first introduced from outside with the inflowing water to be expelled again after a short sojourn inside.
The teredo requires for respiration a clear, pure water. It has often been remarked that piles placed in dirty, muddy water, near drains, for example, are protected thereby. The water should have, moreover, a certain degree of saltness; the teredo cannot live in brackish water; that is a point to which we shall return later.
The teredo continues to grow in the wood; while the gallery which it forms presents near the surface a diameter of only one-quarter to half a millimetre, it enlarges little by little, until it reaches a diameter of five millimetres and more; as regards his length, and consequently that of the tube which incloses him, we have sometimes found it to be thirty to forty centimetres. He never goes upward more than half-way between the flow and ebb of the tide; although the teredo is thus, for a short time, partially above the water, yet it appears that the wood holds a sufficient amount of moisture to sustain his life temporarily.
The researches of Kater have still further shown, what had already been remarked by Sellius, that the teredo can hibernate in the wood, and that it is those individuals, thus preserved, which in the spring go through with all the phenomena of reproduction i.e., the formation of eggs, fecundation, development, and expulsion of the young.
The part of the external integuments which constitutes the mantle deposits a calcareous matter, forming an interior lining to the gallery in the wood (Fig. 12, f); between this calcareous casing and the body of the animal there remains a space sufficient to prevent any inconvenience, at least during the act of respiration; for it is possible that when the teredo absorbs water, which serves for respiration, his body is distended, and fills exactly the calcareous tube. The form of this tube, secreted little by little, corresponds exactly with that of the gallery, which has been slowly perforated in the wood; it has the appearance, also, of a series of rings placed one against the other. As the animal progresses, a new ring is added to those which existed before, so that when the tube is closed at its extremity by a calcareous film, its length represents the total length of the animal (Fig. 12, b to c). Among the segments of the tube, those which are nearest the surface of the wood are the oldest and hardest; in the interior of the wood, where the gallery ends (Fig. 12, g), the calcareous ring, newly formed, is at first soft, flexible, and of slight consistency; later, it becomes solid, and closes up the tube, as has been remarked by Sellius. In the variety of teredo described by us, we have never observed the formation of two openings surrounded by calcareous matter, situated side by side, like an eight placed sidewise, ∞, and serving as a passage for the siphons, as described by Deshayes.
The calcareous tube, once formed, constitutes for each teredo his own abode, where he isolates himself from his companions, and has nothing to fear from their close proximity. One never sees a teredo pierce the tube of another. The tubes make their way side by side, and cross each other in every direction, but, be the wood ever so worm-eaten, there always remains a woody wall, often very thin, it is true, between two adjoining tubes.
The very existence of the adult teredos seems dependent upon the wood. Withdrawn from their galleries and placed in sea-water, they could be kept alive by Kater scarcely more than three or four days. Left in the wood, but taken out of sea-water, they would die within twenty-four hours. Deprived at the same time of contact with wood and sea-water, they perished at the end of one or two hours. In damp wood, that is, wood soaked with salt-water, their existence is prolonged somewhat. Wood and sea-water are, then, both necessary. If these two conditions of existence are furnished them, one can, Kater assures us, keep them alive during several months.
The teredo does not always remain in peaceable enjoyment of the home he has constructed, and the nourishment the water brings to him. Fig. 13. He finds himself exposed to the attacks of an enemy, of an annelide to which the late M. W. de Haan has given the name of Lycoris fucata (Fig. 13). In our day, as well as at former epochs, this annelide is constantly found wherever the teredo exists. His eggs and embryos are met with in the midst of those of that mollusk.
Kater has remarked that the adult annelide, leaving the muddy bottom, where he has hibernated, and in which the piles are driven, climbs along the surface of the wood toward the opening made by the teredo; there he sucks away the life and substance of his victim; then, slightly enlarging the aperture, he penetrates and lodges in place of the teredo. Later the annelide reappears and seeks for new prey. All the early writers on this subject state that they have found this annelide in wood at the same time with the teredo. It is remarkable that a Fig. 13 similar annelide, and perhaps the same, has been found in the cavities hollowed out in stone by the pholades.
It is important that it should be generally understood that this annelide is not only harmless, but renders the greatest service in devouring the wood-destroyer. It is a narrow annelide, ten to fifteen centimetres long, provided on his sides with a great number of small feet terminated with a point and garnished with hairs and showing in front a pair of strong upper jaws, horny and sharp, and lower jaws bent backward in form of hooks and carried outside by the aid of the lower lip, which is developed somewhat like the finger of a glove turned backward. Behind the head are four pairs of tubular-formed gills. With these weapons the annelide pursues and devours the teredo. The observations of Kater teach us that he is generally found in the empty galleries with the remains of the teredo; sometimes even he is seen as if clothed with the integuments of the teredo, while he is occupied in ransacking his intestines. Once Kater had the rare chance (which, by-the-way, only secures such good fortune to very careful observers) to seize the moment when an annelide, coming out of one of the openings of wood, at once took possession of a teredo that he had placed on the bottom of the vessel which held the wood. He saw the annelide seize the teredo with his jaws, draw him into the canal which he occupied, and devour him so completely that there only remained the two valves of the shell.
It is in an entirely different manner that the cirripeds (Balanus sulcatus) aid in preserving wood. When these animals, to which sailors and the inhabitants of our coasts give the name of Pustules of the Sea, or Sea-Thorns, multiply to such an extent on the surface of wood that their disks touch, without leaving the least vacant space, the natural consequence is, that the young teredo cannot find any place where it can attach itself, and hence it is impossible for him to penetrate the wood. This preservative effect is produced even when the shells have fallen, provided the disks adhere to the wood.
On the Circumstances which favor the Ravages of the Teredo.—The commission gave in its first report an historical epitome of the injuries done by the teredo at different epochs in Holland.
When the teredo was remarked for the first time, an idea prevailed that it was imported from abroad; vessels coming from the East Indies were accused of having brought that destructive guest. Two facts show the incorrectness of this idea. On the occasion of the deepening of the Dumbart Dock at Belfast, William Thompson found, twelve feet below the surface of the earth, in a blue, argillaceous soil, the trunk of a tree entirely riddled by the teredo. Considering the depth at which this débris was found, and the fact that it lay beneath a series of strata of shells, it is certain that it was deposited there ages ago, long before a vessel, coming from the East or West, could touch the coast at Belfast.
Fossil wood, perforated by the teredo, has been found in different localities: for example, in the London clay, in the Eocene formations at Brussels, where Van Beneden discovered fossil wood, inclosing the remains of the teredo; and at considerable depth, also, near Ghent, at the time of the construction of the citadel.
The teredo existed in a geological period earlier than our own, and he appears to have been always an inhabitant of our coast. Why is it, then, that at certain epochs, as in the years 1730, 1770, 1827, 1858, and 1859, he multiplied so prodigiously as to destroy entire dikes in a very short space of time? Even as early as 1733, Massuet assigned as a cause an increase of the degree of saltness of the water, resulting from a diminution in the quantity of the rainfall; the same opinion is found expressed in the reports of many chief engineers of Waterstaat. To decide whether this opinion was well founded, careful analyses were made in 1859, which, compared with those made at other epochs, showed that the proportion of salts found in the water of the Y was just double what it was in 1855, and a third more than in 1825.
The three circumstances, under which this exceptional increase of Fig. 14.—This cut was made from a Teredo navalis, taken from a pile exposed two seasons (1876 and 1877) at Horn Island, Gulf of Mexico. When first taken from the wood it was eighteen inches long. the teredo was observed, were a moderate rainfall, and, as a direct or remote consequence, a falling of the level of the rivers, and an increase of the saltness of the water of our arms of the sea. As an additional favoring circumstance should also be noted an increase in the temperature.
Experiments in the Preservation of Wood from the Attacks of the Teredo.—To justly appreciate the experiments tried by the commission, it must be borne in mind that when it was discovered, in 1858 and 1859, that great injury was being done to our marine works by the teredo, very many methods of preservation were recommended on all sides to the Government, and that the nature of many of these remedies was kept secret by the persons extolling them. In order that its labors should offer every guarantee of impartiality, and although convinced in advance of the inefficacy of a large number of the means proposed, the commission decided not to lay aside any without a trial. Moreover, as far as possible, it had the pieces of wood to be experimented with prepared by the inventors or proposers of the processes, in order to protect itself from every accusation of unfairness.
The experiments were made the first year in the ports of Flessingue, Harlingen, Stavoren, and Nieuwendam, and afterward in the ports of Nieuwe-Diep and Stavoren. The woods employed were oak, red fir, ordinary fir, and Pinus sylvestris, generally in pieces one metre long by two or even three decimetres square. These blocks were prepared in different ways, and care was taken to place by their side blocks of the same kinds of wood without any preparation as counter-proofs.
The trials made by the commission may be placed under three principal groups:
1. Coatings applied to the surface of wood, or modifications of the surface itself.
2. Impregnation of wood with different substances, which modify the interior as well as the surface of the wood.
3. Employment of exotic woods, other than ordinary woods of construction.
Coatings applied to the Surface of Wood.—The methods belonging to this group, which have been examined by the commission, are the following:
1. Method invented by M. Claasen, and kept secret by the inventor.
2. Metallic paint, invented by M. Claasen and likewise kept secret.
3. Method of M. Brinkerink, consisting of a mixture of Russian talc, coal-tar, resin, sulphur, and finely-powdered glass, applied hot on wood previously roughened by a toothed instrument; this application was two millemetres thick.
4. Method of M. Rijswijk, analogous to the preceding.
5. Paraffine varnish, obtained by the dry distillation of peat, from the factory of MM. Haages & Co., at Amsterdam.
6. Coal-tar, applied cold on the wood in several successive layers, or applied hot on wood whose surface had been previously carbonized. Some pieces were treated as follows: Holes were first bored in them and filled with tar, then plugs were fitted closely to the holes and driven in with sufficient force to make the tar penetrate the wood; other pieces still were painted over with a mixture of tar with sulphuric acid, or sal ammoniac, or turpentine, or linseed-oil.
7. Painting with colors mixed with turpentine and linseed-oil—among others with chrome-green or with verdigris.
8. Singeing or superficial carbonization of the wood.
The pieces of wood thus prepared were placed in the water at the end of May, 1859, and the first examination, made toward the end of September of the same year, showed that neither of these methods afforded any protection from destruction by the teredo. There was one partial exception, and that was the pieces of wood treated according to No. 6; these showed only traces of the teredo here and there. But, at a later examination, in the autumn of 1860, when the wood had been exposed a year and a half, these were also found to be equally severely attacked by the teredo.
The results of these experiments strongly convinced the commission that no exterior application of any nature whatever, or modification of the surface merely, would give any efficacious guarantee of protection against the teredo. Even supposing that one or another of these means would prevent the young teredos from attaching themselves to the wood, yet the constant friction of the water or ice, or any accident, might break the surface of the wood sufficiently to give access to the teredo.
This seems a proper place to mention a practice in general use in Holland for warding off the teredo: this consists in covering wood with a coat-of-mail made of nails. This operation is very costly; for, to really protect wood in this way, it is important that the square heads of the nails join exactly; for insuring the best results, the armored piles are exposed in the open air for some time before being placed in the water, that rust, forming on the surface of the iron, may close up the interstices inevitably remaining between the heads of the nails. But this precaution is not infallible, as the commission examined piles more than once, in the course of its investigation, which had been several years in the water, and whose surface was entirely incrusted with rust more than a centimetre thick, but which were, nevertheless, eaten in the interior by the teredo.
Sluice-gates are frequently covered by sheets of iron, copper, or zinc. It is evident that, so long as such covering remains intact, there is no cause for anxiety on the score of the teredo. Unfortunately, experience has taught us that this protection is not permanent, but is rendered ineffectual by being broken by the force of the water or blocks of ice.
Nature affords sometimes, as we have seen above, a more efficacious protection in covering wood with barnacles or other shell-fish, with the condition that this covering be made before the young teredo attaches itself to the wood. Facts of this sort have led Lehmann to propose the planting on wood of the common mussel (Mytilus edulis).
Impregnation of Wood with Different Substances.—The commission examined in this category the following methods:
1. Sulphate of Copper.—The impregnation of the blocks with this salt was performed at the factory of MM. Van der Elst and Smit, at Amsterdam. Experience proved, even in the first summer (of 1859), that this preparation had absolutely no power against the teredo. Nevertheless, to make sure that the failure of this experiment was not due to insufficient preparation, the commission procured from the establishment of M. Boucherie, at Paris, two pieces of beech-wood covered with its bark, two pieces of beech without bark, and two pieces of pine, all prepared with sulphate of copper. These blocks, when exposed, did not resist the teredo any better than those prepared at Amsterdam. These trials completely confirmed the results obtained by the engineer Noyon (“On the Inefficacy of the Boucherie Process in Sea-Water,” Annals of Bridges and Roads, April, 1859).
2. Sulphate of Protoxide of Iron (Green Vitriol).—The blocks were impregnated with this salt at the establishment of MM. Van der Elst and Smit. The first summer proved that this method would not in the least prevent the wood from being destroyed by the teredo. And the same was true of the following method:
3. Acetate of Lead.—The blocks impregnated with this salt were prepared at the same establishment.
Surprise may be expressed that the commission did not try experiments with corrosive sublimate. It felt that it could dispense with them, as its inefficacy had already been sufficiently established by previous experiments on a large scale at the marine dock-yards at Rotterdam. Experiments with mercurial and arsenical salts were tried, in 1730 and later, but without satisfactory results.
4. Soluble Glass and Chloride of Calcium.—Pieces of oak and red fir were impregnated at the same establishment at Amsterdam, first with a solution of soluble glass (silicate of soda), and afterward with a solution of chloride of calcium; the object of this double impregnation was to produce in the pores of the
Fig. 15.—This cut was made from a piece of pine-slab, partially creosoted and exposed one season (1877) in the Gulf of Mexico. Only the dark-colored portion on the right side of the block was creosoted for this experiment. The rest of the block, untreated, was entirely riddled by the Teredo navalis, up to the edge of the creosoted portion, but that the destructive marine worm carefully avoided.
wood a silicate of lime. The pieces thus prepared were left in the open air during six months before being placed in the water, in order that the chemical combination might be as complete as possible. These pieces were exposed in the water at Nieuwe-Diep, in March, 1862, and when withdrawn, in October of the same year, the preparation was found to be powerless as a protection against the teredo.
5. Oil of Paraffine.—The firm of Haages & Co., at Amsterdam delivered to the commission some pieces of oak and red fir injected with a substance produced by the dry distillation of peat, to which they gave the name of oil of paraffine. In the month of July, 1860, the commission placed at Stavoren and Nieuwe-Diep ten pieces thus prepared. They were examined in the course of the same year, after they had passed one summer in the water, and it was found that they had resisted the attacks of the teredo.
The commission conducted all its experiments thus: They placed in the water ten pieces of each variety of wood, treated according to the prescribed method, so that they could withdraw each year, during ten consecutive years, one of the pieces to be submitted to examination. In making the examination, they removed with an adze the outside of the wood to a depth of some millimetres, which was sufficient to show the galleries of the teredos, if there were any. The pieces found intact were replaced in the water, and the following year their condition was tested in the same way, by removing the shavings as before. By this plan the commission felt certain that, if the blocks were not injured by the teredo during several successive years, they did not owe that protection to a superficial covering, but that the wood itself resisted the destructive efforts of the teredo, and that there would be no reason for fearing that piles, prepared in a similar manner, would, at any time, lose their power of resistance, when injured on their surface by water or ice, or by slow dissolution of the active principle of the preservative substance.
When the pieces of wood treated with oil of paraffine were taken from the water in 1862, after a sojourn of more than two years, or rather during three summers, traces of the teredo were found in the pieces of oak, but not on those of red fir; but when examined in November, 1863, fully-developed teredos were found everywhere, in the fir as well as in the oak, in the pieces whose surfaces had been removed by the adze, but not more than in those which had not been submitted to any examination.
6. Oil of Creosote.—This is, as is very well known, a product of the dry distillation of coal-tar, separated by distillation from the more volatile parts, which serve for the preparation of benzole and naphtha, the residuum being pitch. Experiments had already been tried abroad, as well as in Holland, with this substance, and from the beginning of their experiments the commission paid especial attention to this very important method of preparation.
Wood of various kinds, prepared with creosote-oil at the works of the Society for the Preparation and Preservation of Wood, at Amsterdam, was placed in the sea. in the month of May, 1859, at Flessingue, Harlingen, and Stavoren. In the month of September following, at Flessingue, the pieces of oak, pine, and red fir, were found intact, while those unprepared were perforated. In the month of October, of the same year, the pieces of creosoted pine and fir at Harlingen showed a perfect state of preservation. At Harlingen the treated and untreated pieces were fastened together; the teredo penetrated the latter, but had not touched the creosoted wood. The same was true of the creosoted wood exposed at Stavoren, when visited in 1859.
At Nieuwendam, in March, 1859, three pieces each of oak, pine, and red fir, all creosoted at Amsterdam, were exposed in the sea. They were examined in September of the same year. They had been fastened together by cross-pieces of unprepared wood: it was found that the teredo had penetrated, at the juncture of these cross-pieces, even into the creosoted wood, and that sometimes he stopped immediately beneath the surface, at others he penetrated to a depth of several millimetres; in the oak, he worked his way into the interior through those parts of the surface which were not in contact with the unprepared wood.
Experiments with creosote-oil were recommenced in July, 1860, with ten pieces each of oak and red fir, following the plan indicated in paragraph 5; the localities chosen were Nieuwe-Diep and Stavoren; in the latter place the pieces which remained intact the previous year were again placed in the water after their surface had been removed by the adze. Still later, in August, 1861, a further trial was made at these same places with pieces of pine, beech, and poplar, sent to the commission by Mr. Boulton, and prepared at his works in London.
All these pieces were examined toward autumn in 1862, 1863, and 1864; while the unprepared pieces, placed near the others as counter-proofs, were found each year filled with teredos, one could not discover any traces of the teredo in the creosoted pieces except in the oak creosoted at Amsterdam; in cutting these, it was found that the creosote had penetrated them very imperfectly.
A third examination, in 1864, showed that all the pieces prepared by Mr. Boulton, and which had been exposed in the sea since August, 1861, were entirely intact; the most careful examination could not show the slightest trace of the worm, even in the pieces withdrawn from the water in 1862 and 1863, and each time scraped to a depth of several millimetres and again placed in the water. They resisted the attacks of the teredo perfectly.
An equally favorable and decisive result was obtained from the pieces of fir creosoted at Amsterdam. Notwithstanding they had been exposed in the sea since July, 1860, during five consecutive summers, nothing could be discovered which resembled the galleries of the teredo: one of the pieces, at a point where the color of the wood indicated an insufficient penetration of the creosote-oil, showed a very slight worm-eaten appearance; but the absence of the calcareous deposit, and the whole character of the opening, indicated clearly that it should be attributed to some other animal than a teredo.
As to the unprepared pieces, there only remained small ends, which reached above the water. All the rest was converted into a spongy mass, which broke at the slightest effort.
The experiment with the creosoted oak was less satisfactory. In all the pieces were found, here and there, galleries of the teredo, but always in small numbers; in sawing the wood, it was found that the injuries were invariably in those parts where the color showed that the oil had not been able to penetrate. Although, as far as is known, no effort has been made elsewhere to preserve oak from the teredo, the commission places great value upon experiments with this wood. In fact, for many marine works, oak cannot be replaced by any soft wood which absorbs creosote-oil easily. Hence, the commission has had creosoted at Amsterdam, by a newly-perfected process, some pieces of oak, which were exposed in 1864 at Nieuwe-Diep; these will not be examined until tested during three summers.
Petroleum has also been recommended to the commission, but it was not deemed worth while to experiment with it, especially on account of its high price; even although petroleum should prove to be as efficacious as creosote-oil for protecting wood against the teredo, its price would prevent its use for that purpose.
Experiments with Exotic Woods, other than Ordinary Woods of Construction.—The commission has not been able to make many experiments in this direction. It acquired a certainty that the greenhart of Surinam, the bulletrie, the American oaks, and wood as hard as mamberklak, are not spared by the teredo. The commission received a large piece of the wood of guaiacum, which had been five or six years in the water at Curacoa, and was found to be entirely eaten by the teredo—an evident proof that even the hardest woods are not safe from the attacks of that mollusk.
The commission has received, it is true, many communications relative to different kinds of woods known to be poisonous to fish, but it has not had an opportunity to experiment with them. We await some light on this point, from researches which the Government has ordered to be made at our possessions in both the East and West Indies.
Conclusions.—By way of recapitulation, the results of the experiments, tried by the commission during six consecutive years, were as follows:
1. The different coatings applied to the surface of wood, with the design of covering it with an envelope on which the young teredo cannot attach itself, offer only an insufficient protection; these coverings are likely to be injured either by mechanical means, such as the action of the water, or by being dissolved by the water. Just so soon as a point of surface of the wood is uncovered, be it ever so small, the teredo, still microscopic, penetrates into the interior. Covering wood with sheets of copper or zinc, or with nails, is a too expensive process, and only protects the wood so long as they form an unbroken surface.
2. Impregnation with inorganic, soluble salts, generally considered poisonous to fish and animals, does not protect wood from the attacks of the teredo. This want of efficacy must be attributed in part to the fact that the salts absorbed by the wood are extracted by the dissolving action of sea-water, and in part, also, because those salts do not appear to have a poisonous effect upon the teredo.
3. Although we do not know with any certainty if, among exotic woods, there may not be found those which will resist the teredo, we can affirm that hardness is not an obstacle which prevents that mollusk from perforating his galleries; the ravages observed in the wood of guaiacum and mamberklak prove this.
4. The only means which can be regarded with great certainty as a true preservative against the injury to which wood is exposed from the teredo, is the oil of creosote; nevertheless, in employing this means, care is necessary that the oil be of good quality, that the impregnation be thorough, and that such woods be used as will absorb oil readily.
The conclusions arrived at by our commission are confirmed by the experience of a large number of engineers in the Netherlands, and also in England, France, and Belgium. M. Crepin, a celebrated Belgian engineer, expresses himself thus, in a report on experiments tried at Ostend, under date of February 5, 1864:
“The result of our experiments now seems decisive, and we think we can draw from them this conclusion: that soft woods, well prepared with creosote, are protected from the attacks of the teredo, and are in a condition to assure a long duration. The whole matter, in our opinion, is reduced to a question of thorough impregnation with good creosote-oils, and the use of such woods as are adapted to the purpose. It has been found that resinous  woods are impregnated much better than other varieties.”
M. Forestier, a French engineer at Napoléon-Vendée, in a report dated March 3, 1864, makes a résumé of experiments conducted by himself in the port of Sables-d'Olonne, in the following words:
“These results fully confirm those established at Ostend, and it seems to us difficult to refuse to admit that the experiments at Ostend and Sables-d'Olonne are decisive, and prove in an incontestable manner that the teredo will not attack wood properly creosoted.”
Under date of Haarlem, April 20, 1878, Prof. Von Baumhauer writes to Edward R. Andrews, of Boston:
“I have deferred answering your favor of the 22d of February until I hadcorresponded with the chief-engineers of the Waterstaat as to the results obtained in their experience in the use of cresoted timber in all our marine works, in large quantities and during some tens of years. They all unanimously agree that the teredo will not penetrate timber thoroughly impregnated with creosote; but that, to obtain the best results, the work must be thorough, as they had observed that the teredo had destroyed piles only superficially injected.
“Fir, if the sap be first withdrawn in a vacuum and then treated with hot oils under a heavy pressure, can be most thoroughly creosoted; but oak is more difficult. Still, I have often seen heavy oak-piles where the creosote had entered into the very heart.
“Creosoted wood is also used in our country for railway-sleepers and tramways, and everywhere with the best results. They last four or five times longer than when unprepared, while experience shows that wood treated with sulphate of copper or chloride of zinc (Burnettizing) is neither protected from the teredo nor the influences of humidity and of the atmosphere.”