IMMUNITY AND SUSCEPTIBILITY. 107 



ceptible of further division into groups according to their 

 mode of action; thus, if they act destructively upon the 

 bacteria they are called micosozins and micophylaxins. 

 If they neutralize bacterial toxins, they are called toxo- 

 sozins and toxophylaxins. 



The existence of toxosozins and toxophylaxins is, how- 

 ever, a matter of theory, not of demonstration; and until 

 it can be shown that there are such bodies able to operate 

 successfully against poisons in large doses, immunity will 

 not be explained. 



At present, in the absence of any explanation of the 

 ability of an animal to endure the bacterial intoxication, 

 it is evident that immunity remains unexplained, and the 

 conclusion of Sternberg \ that "natural immunity is due 

 to a germicidal substance present in the blood serum 

 which has its origin (chiefly at least) in the leukocytes 

 and is soluble only in an alkaline medium," must be 

 rejected as explaining only a part of the phenomena. 



Modification of Immunity. — Immunity is neither per- 

 manent nor constant, but varies with many natural and 

 artificial conditions. Thus, it is found that young ani- 

 mals are, as a rule, much more susceptible to the in- 

 fectious diseases than the adult animals. It is also 

 found that newly-born animals are sometimes immune 

 to diseases to which they will later become suscept- 

 ible. 



I. Reduction of Immunity. — Any condition or combi- 

 nation of conditions depressing the general vitality lessens 

 the power of resisting infection 



a. Depressing hygienic conditions have long been asso- 

 ciated with the occurrence of disease, and it is well estab- 

 lished, both clinically and statistically, that infectious 

 diseases are most common and severe where overcrowd- 

 ln ») P oor ventilation, improper diet, overwork, and insuf- 

 ficient sleep exist. 



b. Noxious gases. — It has long been supposed that 

 sewer-gas and other poisonous gases predispose "to disease. 



1 Immunity and Serum- Therapy, 1895. 



