BLOOD 735 explimauon of the production of this coat. The red corpuscles have a density superior to that of the liquor sanguinis, and when the blood is at rest they naturally sink until an obstacle prevents their doing so. As long as coagula- tion has not begun, the globules move toward the bottom of the vessel ; and when fibrine forms the solid shreds which constitute the co- agulum, the upper layer of the mass of the blood no more contains red corpuscles, and therefore is colorless. Now, in inflammation the sinking power of the red globules is in- creased, so that the colorless layer of coagu- lated fibrine is thicker than in other cases, and thus it is that the huffy coat and its thickness are sometimes a good indication of the exist- ence and even of the degree of an inflammation. But there are many circumstances besides in- flammation and without it which lead to the production of the huffy coat. Andral has shown that when the proportion of red corpus- cles is diminished in the blood, the buff exists frequently on the top of a small clot. This is the case in chlorosis, in anaemia, &c. Another circumstance which favors the formation of a colorless layer of coagulated fibrine is the aggregation of the red corpuscles in columns or piles (like piles of coin), which renders them heavier and increases their speed in sink- ing. In inflammation, as shown by II. N"asse, Wharton Jones, and others, the red corpuscles have an increased tendency to aggregate, and this explains why the buffy coat is so frequent- ly thick in inflammation. Lehmann has shown, however, that all the circumstances which have been considered as favorable to the sinking of the red corpuscles, and to the formation of the buffy coat, are insufficient to explain the facts in all cases, and that there are some unknown causes of production of the buff. 12. The coagulation of blood does not generate heat, as has been imagined. The ex- periments of John Davy, and especially those of Denis, afford convincing proofs in this respect. VI. FORMATION OF THE BLOOD. We shall not examine here the first formation of this liquid, that is, its production in embryos ; this subject belongs to the article EMBRYOLOGY. We shall only inquire into the sources of the blood, and the mode of production of its principal materi- als, in completely developed animals. Three sources exist for the formation of the various materials composing the blood: 1, the body; 2, the food ; 3, the respiration. That the body itself is a source of blood we cannot doubt. If, as Piorry has shown, we take blood from a dog in such quantity that we cannot abstract one or two ounces more without killing the animal, we find the next day, although the dog has not been fed, that we may take out again 10 or 12 ounces of blood without causing death. It follows from this fact that a forma- tion of blood has occurred, and, as there has been no food taken, the blood formed must come from the body. As regards the share of respiration in the formation of blood, we shall 99 VOL. ii. i7 only remark here that it gives certain gases, | especially oxygen. For more details on the influence of oxygen and other gases on the
- blood, see RESPIRATION. The formation of
blood is very rapid when abundant and very nutritive food is taken, as is proved by the fol- lowing facts, most of which are related by Hal- ler. For several years a young girl was bled sometimes every day, at other times every other day ; a hysterical woman was bled 1,020 times in 19 years ; another individual had a loss of 1,000 Ibs. of blood in a year ; in another, 5 Ibs. of blood were lost every day for 62 days ; a young man had a loss of 75 Ibs. of blood in 10 days; an Italian physician, Dr. Oavalli, relates that a woman was bled 3,500 times in 28 years ! It seems from these facts, and from many others, that the power of formation of blood increases with the frequency of the losses of this liquid, and with the habit of repairing these losses. The food, before being able to repair the losses of blood or to give to this liquid the materials which it fur- nishes to the tissues, must be modified by diges- tion, and brought to the blood by absorption, either directly or by the lymphatic vessels. The part of the food absorbed by these vessels is called chyle. The transformation of lymph and chyle into blood is an act of much great- er magnitude than was formerly supposed. According to the researches of Bidder and Schmidt, there is about 28'6 Ibs. of lymph and chyle poured into the blood of a man daily, i. e., from one sixth to one seventh of the weight of the body. Of this amount 6'6 Ibs. are true chyle, and 22 Ibs. are true lymph. In these two liquids elements similar to those of the blood are found : i. e., water, salts, fats, albu- men, fibrine, and corpuscles. This shows that the work of formation of blood from chyle, as well as lymph, is not very considerable; in other words, the transformation of food into blood is already much advanced in the bowels and in the lymphatic vessels. One of the most interesting questions relative to the formation of the blood is that of the origin of the blood corpuscles. In the first place, as regards the colorless corpuscles of the blood, there is now no doubt that they are entirely similar to the lymph corpuscles, and that they have been brought into the blood with the lymph and chyle. As regards their formation, see LYMPH. The source of the albumen of the blood is chiefly the food, and it is brought into the cir- culation by direct absorption by the veins in the stomach and bowels, and only partly by the chyle. The origin of the fibrine of the blood is not exclusively the food, as some phys- iologists maintain. It must come from the tis- sues or from the albuminous matters of the blood, for Brown-S6quard has proved that when blood deprived of fibrine is injected into the arteries of a limb, the veins give out blood containing fibrine, and in greater quantity if the limb is galvanized. Besides, it is known that in animals deprived of food, or bled many
