Simon Flexner and Noguchi[80] have studied the action of the serums of _Crotalus_, _Ancistrodon_, and a non-poisonous species, the pine snake (_Pituophis catenifer_), on the venoms of _Naja_, _Ancistrodon_, and _Crotalus_. They found that the serum of _Crotalus_ rapidly dissolves the red corpuscles of man, the dog, rabbit, guinea-pig, sheep, rat, pigeon, and horse. The serum of the pine snake affects the same red corpuscles, but in a lesser degree. Heating to 58° C. suppresses the hæmolytic power of these serums, but they can be restored to activity by the addition of a very small quantity of the same serum in a fresh condition, of fresh serum derived from other snakes, or of fresh serum from the guinea-pig. Antivenomous serum also, when added in a suitable dose, entirely suppresses the hæmolytic action of snake-serums; it has, however, greater effect upon the hæmolysin of _Cobra_-blood than upon that of the blood of other snakes. This observation had previously been made by W. Stephens,[81] and it has been verified by Noc in my laboratory. _Crotalus_-serum dissolves the red corpuscles of the mongoose (_Herpestes ichneumon_) of Jamaica, whose extraordinary resistance to venom is well known. But if variable doses of _Ancistrodon_-venom and _Crotalus_-serum be made to act simultaneously upon these corpuscles, the latter are no longer dissolved. Again, if, instead of red corpuscles which are but little sensitive, like those of the mongoose, we employ the highly sensitive corpuscles of the guinea-pig, the result is the same. These experiments are regarded by Flexner and Noguchi as proving that the amboceptors of the toxic serum become fixed, in conformity with Ehrlich’s theory of the lateral chains, upon the receptors of the sensitive erythrocytes, and leave no more receptors free for the fixation of the venom. The same investigators have endeavoured to determine the respective toxicity of the tissues of the different organs of _Crotalus_. They found that the most toxic organs are the spleen and the liver; the toxicity of the spinal cord, kidney and muscles is much less. It appears that this toxicity is intimately connected with the quantity of blood that the tissues retain, for the physiological effects observed are identical with those that follow the injection of blood or serum alone. They also ascertained that the contents of the eggs of _Crotalus_ are especially rich in poison, and this poison appears to consist for the most part of _neurotoxin_, since it does not cause hæmorrhages. Phisalix has observed that the ovules of the viper exhibit analogous toxicity.[82] Summing up what has been stated above, we find that the blood of both poisonous and non-poisonous snakes contains toxic substances, destructible by heating to 68° C., and physiologically distinct from venoms, but like the latter possessing the property of dissolving the red corpuscles of the majority of vertebrates and of producing hæmorrhages. CHAPTER XI.