SUSCEPTIBILITY AND RESISTANCE. 125 



white mice enjoy a high degree of immunity, and so on. 

 Then there are diseases, of which leprosy is a good example, 

 which appear to be peculiar to the human subject and 

 have not yet been transmitted to animals. And further, 

 there are others, such as cholera and typhoid, which do not 

 naturally affect animals, and the typical lesions of which cannot 

 be experimentally reproduced in them, or appear only imper- 

 fectly, though pathogenic effects follow inoculation with the 

 organisms. In the case of the human subject, differences 

 in susceptibility to a certain disease are found amongst 

 different races and also amongst individuals of the same 

 race, as is well seen in the case of tubercle and other 

 diseases. Age also plays an important part, young subjects 

 being more liable to certain diseases, e.g., to diphtheria. 

 Further, at different periods of life certain parts of the 

 body are more susceptible, for example, in early life, the 

 bones and joints to tubercular and acute suppurative 

 affections. 



The natural resistance or immunity possessed by an 

 animal may be artificially lowered by certain methods, of 

 which the following well -recognised examples may be 

 given. Frogs, which are naturally immune to anthrax, can 

 be rendered susceptible to infection by being kept at a 

 temperature of about 35 C. Rats naturally immune can 

 be rendered susceptible to glanders by being fed with 

 phloridzin, which produces a sort of diabetes, a large 

 amount of sugar being excreted in the urine. (Leo.) 

 Guinea-pigs may resist subcutaneous injection of a certain 

 dose of the typhoid bacillus, but if at the same time a 

 sterilised culture of the bacillus coli be injected into the 

 peritoneum, they quickly die of a general infection. Also 

 a local susceptibility may be produced by injuring or 

 diminishing the vitality of a part. If, for example, previous 

 to an intravenous injection of staphylococci, the aortic 

 cusps of a rabbit be injured, the organisms may settle 

 there and set up an ulcerative endocarditis, or if a bone be 

 injured, they may produce suppuration at the part, whereas 

 in ordinary circumstances these lesions would not take 



