TOXINS AND ANTITOXINS 75 



duce a somewhat similar poison in addition to formic acid. The 

 " black flies " of the woods produce a poison not as yet identified, 

 but no poison has as yet been isolated from the mosquito. Numer- 

 ous other insects appear to have poisonous secretions, but as yet no 

 studies have been made in detail as to their isolation and identification. 



Toads, frogs, and salamanders produce dermal secretions which 

 are poisonous, several of which operate like digitalis and some like 

 epinephrin. These poisons are interesting from a pharmacological 

 point of view, but as they are not capable of producing immune re- 

 actions in animals they deserve no extensive discussion here. 



Poisonous fish comprise several groups. One group secrete 

 poisons in special glands, the poison being discharged through 

 spines. Such poisons contain a hemolysin which requires an 

 activator, as in the case of cobra- venom hemolysins. These poisons 

 act as powerful local irritants and as cardiac depressants and may 

 cause death. Only one variety of fish produces poisoning by its 

 bite, the poison being secreted in the gums. Other fish are poison- 

 ous when eaten even when quite fresh, the poison being found 

 especially in the ova and ovaries. The symptoms may be of a 

 severe choleriform type frequently fatal, or of a less severe gastro- 

 intestinal type, not commonly leading to death. Certain fish, par- 

 ticularly in the tropics, rapidly decompose with the formation of 

 poisonous products or ptomains. The bites of crabs may produce 

 peculiar erysipelas-like lesions or " erysipeloid," but the origin and 

 nature of the poison are not known. Many individuals develop 

 toxic symptoms after eating shell-fish and other sea food, in some 

 cases due to the decomposition of the food, but in most instances 

 due to a peculiar hypersusceptibility which will be discussed under 

 Hypersusceptibility (see page 230). 



Eel serum deserves special consideration because of the fact that 

 immune bodies can be produced. It is not poisonous when ingested, 

 but is highly so if given intravenously and it produces conjunctivitis 

 when instilled into the sac. Relatively large doses lead to rapid 

 death and small doses may produce cachexia and death after sev- 

 eral days. The toxic 'element is in the albumin fraction of the 

 serum and is destroyed by 58 C. for fifteen minutes. It contains 

 a hemolysin and probably also a neurotoxin. The hemolysin does 

 not act as an amboceptor, reactivation by fresh serum being im- 

 possible after the eel serum has been heated. Immune sera can be 

 produced which neutralize the hemolysin in vitro and also protect 

 animals from death by the eel serum. The serum of lampreys and 

 rays is similarly toxic. 



The parasitic protozoa and other animal parasites are strikingly 

 free from substances which induce immunity. The protozoa show 

 few exceptions to this rule. Cytolysins can be produced experi- 

 mentally for amebse, but no such reaction takes place in human 

 patients. Active immunity to trypanosome infection can be pro- 



