90 Immunity 



have more or less resemblance to one another; thus, anthrax is 

 essentially a disease of warm-blooded animals, though certain 

 exceptions are observed, and Metschnikoff has found that hippo- 

 campi (sea-horses), perch, crickets, and certain mussels are sus- 

 ceptible. Among the warm-blooded animals anthrax is most fre- 

 quent among the herbivora, though some carnivora may also be 

 infected. 



Close relationship is not, however, a guarantee that animals 

 will behave similarly toward infection. The rabbit, guinea-pig, 

 and the rat are rodents, but though the rabbit and guinea-pig are 

 susceptible to anthrax, the rat is immune. This is still better 

 exemplified in the susceptibility of mice to glanders. The field- 

 mouse seems to be the most susceptible of all animals to infection 

 with Bacillus mallei; the house mouse is much less susceptible, and 

 the white mouse is immune. Mosquitos, though closely related, 

 are different in their immunity to the malarial parasite. The 

 culex does not harbor the parasite at all, and of the anopheles, two 

 very similar species seem to behave very differently. Anopheles 

 maculipennis being the common definitive host of the parasite, 

 while Anopheles punctipennis is not known to be susceptible to it. 

 The same differences may exist among the members of the human 

 species. It has been asserted that Mongolians, and especially 

 Japanese, are immune against scarlatina, and that negroes are 

 immune against yellow fever, but increasing information is to the 

 contrary. 



Human beings suffer from typhoid, cholera, measles, scarlatina, 

 yellow fever, varicella, and numerous other diseases unknown among 

 the lower animals, even those domestic animals with which they 

 come in close contact. They also suffer from Malta fever, anthrax, 

 rabies, glanders, bubonic plague, and tuberculosis, which are common 

 among the lower animals. Animals, in turn, suffer from distemper, 

 septicemia, etc., the respective micro-organisms of which are not 

 known to infect man. 



It has already been pointed out that mongooses and hedgehogs 

 are immune against the venom of serpents from which other animals 

 quickly die. The tobacco-worm lives solely upon tobacco-leaves, 

 the juice of which is intensely poisonous to higher animals, and is 

 also a good insecticide. Boxed cigars and baled tobacco are often 

 ruined by the larvae of a small beetle that feeds upon them, and a 

 glance over the poisonous vegetables will show that few of them 

 escape the attacks of insects immune against their juices. 



These facts are sufficient to show that many animals are by 

 nature immune against the invasion of microparasites of certain 

 kinds, and that they are also at times immune against poisons. 

 Immunity against one kind of infection or intoxication is, however, 

 entirely independent of all other infections and intoxications. Im- 

 munity against infection usually guarantees exemption from the 



