SCALED REPTILES SNAKES. 415 



Anything that can check this frightful mortality must be welcomed ; and, 

 after the trial of many so-called remedies, it appears that a real antidote is the 

 blood-serum of animals which have been previously immunised to snake- 

 poison or in that of venomous serpents themselves. Regarding the former 

 method, Dr. J. G. M'Pherson writes that its discoverer Professor Fraser of 

 Edinburgh first proved that there is a certain amount of toleration for 

 snake-poison in animals. " Having ascertained the minimum dose required 

 to cause the death of an animal, he started below that amount and gradually 

 increased the dose after intervals of ten days. By this process of gradual .n- 

 creases in the dose of the snake-poison, he found the animal receiving is 

 much at one time as fifty times the amount of the minimum lethal dose with- 

 out it causing any perceptible bad effects. In fact, its general health 

 seemed to improve, as he had the animals weighed once and sometimes twice 

 every day ; and all the time he was administering the venom there was a 

 steady increase in weight. In the meantime Professor Fraser has not carried 

 his experiments of quantity further than fifty times the minimum lethal dose 

 at one time ; but still, when he had got to that point, the animal was receiv- 

 ing in a single dose, without being affected, enough to kill fifty animals of the 

 same size and weight. One of the animals which he had treated by this 

 gradually increasing quantity had, in two months, received enough poison to 

 kill three hundred and seventy fresh animals of equal size and weight, sup- 

 posing that each just got the minimum lethal dose. He then described a 

 second series of experiments in which he used the blood-serum of these 

 animals which had been immunised as an antidote for the venom. He mixed 

 an equal part of this blood -serum and venom together, and injected the mix, 

 ture into a fresh animal. This produced no effect, the serum counteracting 

 the action of the poison. Next he injected some of the immunised blood- 

 serum, which he has named antivenine, into a fresh animal, and then some 

 venom afterwards, but the serum hindered any action of the venom. Then 

 he took another fresh animal and injected the venom, waiting till symptoms 

 of poisoning were manifest ; at once he injected his antivenitie, and put a stop 

 to any further progress of the poisoning. The same results took place after 

 many experiments. All this points to the conclusion that this antivenine, or 

 blood-serum, in an animal that has been able to stand with impunity fifty 

 lethal doses at a time by the increasing dose process is really an antidote to 

 the poison of snakes." Subsequent experiments have shown, as was not 

 unanticipated, that the blood-serum of venomous snakes is likewise an anti- 

 dote to their own poison. 



Nearly all snakes feed upon the bodies of animals that they have killed 

 themselves, the few exceptions to this rule subsisting on eggs. Owing to the 

 extensile structure of the mouth and jaws, already mentioned, as well as to 

 the separation of the lower ejvls of the ribs, and the power of extension exist- 

 ing in the stomach, snakes c,in devour animals of larger circumference than 

 the ordinary girth of their own bodies. Both absolutely and proportionately 

 the largest animals are swallowed by the pythons and boas ; and as these 

 snakes kill their prey by encircling it in the folds of their bodies, and thus 

 crushing it to death, the carcase is rendered soft and plastic, and thus more 

 easily swallowed than would otherwise be the case. Occasionally these ser- 

 pents will swallow members of their own species, as happened not long ago 

 in the menagerie of the Zoological Society of London. In this instance, two 

 large boas occupied the same compartment in the reptile-house, the one 

 measuring nine and the other eight feet in length. One night the two were 



