Page:Popular Science Monthly Volume 14.djvu/333

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319
BEGINNING OF NERVES.

they cease altogether, the animals remaining at the bottom of the water, apparently quite dead. No form or degree of stimulation will now elicit the slightest response; and this fact, it must be remembered, is quite as remarkable in the case of the Medusæ as in that of any other animal. Recovery in normal sea-water is exceedingly rapid, especially in the case of chloroform and ether.

The effects of strychnia may be best observed on a species called Gyancæ capillata, from the fact that, in water kept at a constant temperature, the ordinary swimming motions of this animal are as regular and sustained as the beating of a heart. But soon after the water has been poisoned with strychnia, unmistakable signs of irregularity in the swimming motions begin to show themselves. Gradually these signs of irregularity become more and more pronounced, until at last they develop into well-marked convulsions. The convulsions show themselves in the form of extreme deviations from the natural rhythm of this animal's motion. Instead of the heart-like regularity with which systole and diastole follow one another in the unpoisoned animal, we may now observe prolonged periods of violent contraction, amounting in fact to tonic spasm; and even when this spasm is momentarily relieved, the relaxation has no time to assert itself properly before another spasm supervenes. Moreover, these convulsions are very plainly of a paroxysmal nature; for after they have lasted from five to ten minutes, a short period of absolute repose comes on, during which the jelly-fish expands to its full dimensions, falls to the bottom of the water in which it is contained, and looks in every way like a dead animal. Very soon, however, another paroxysm sets in, and so on—prolonged periods of convulsion alternating with shorter periods of repose for several hours, until finally death puts an end to all these symptoms so characteristic of strychnine-poisoning in the higher animals.

Similarly, without going into tedious details, I may say in general terms that I have tried caffein, nitrite of anyl, nicotin, veratrium, digitalin, atropin, curare, cyanide of potassium, alcohol, as well as other poisons; and almost without any exception I find them to produce the same effects on the Medusæ as they severally produce on the higher animals. The case of alcohol is particularly interesting, not only because an intoxicated jelly-fish is a ludicrous object to observe, but also because the experiments with alcohol show how precisely the specific gravity of the Medusæ is adjusted to that of the sea-water. For if, after a jelly-fish has become tolerably well drunk by immersion in a mixture of alcohol-and-water, it is transferred to normal sea-water, the exceedingly small amount of alcohol which it has imbibed is sufficient to make the animal remain permanently floating at the surface of the water until it again gets rid of the alcohol by osmosis.

As my space is now at an end, I must postpone for the present my account of a number of other experiments which, in point of interest, though not in point of systematic arrangement, have a better claim to