NATURAL IMMUNITY. 



149 



The special features of the phagocytic theory of 

 immunity are considered in a later chapter. For 

 many details in regard to inflammation, the reader 

 is referred to the classic article of Adami on this 

 subject in the first volume of Allbutt's "System of 

 Medicine." 



B. Properties of the Serum and Plasma. 



We have seen that the protection afforded by 

 the body surfaces may be effective against both 

 microbes and their toxins, and that local inflam- 

 matory processes, although most certainly antago- 

 nizing the bacteria, may at the same time have 

 some antitoxic value. 



The term "natural immunity," however, as indi- 

 cated in the preceding chapter, has a peculiar appli- 

 cation to the natural resistance of some species or 

 races of animals to infections to which other spe- 

 cies or races are susceptible ; and to an unusual in- 

 dividual resistance often seen in members of a 

 given race or species. This condition depends on 

 properties residing in the tissues or fluids of the 

 body, and consequently is independent of any pro- 

 tection which the body surfaces afford. Its pres- 

 ence is demonstrated in the most striking man- 

 ner by the experimental method, when micro-or- 

 ganisms or toxins are injected directly into the tis- 

 sues or circulation. At the same time every-day 

 observation provides many examples. 



In certain instances natural immunity or sus- 

 ceptibility shows a relation to zoological affinities. 

 Thus only man and the higher apes are susceptible 

 to syphilis; and only animals which are closely 

 related to cattle, as sheep, goats and other rumi- 

 nants, suffer from rinderpest. There are many 



Natural 



Immunity. 



Zoological 

 Relation- 

 ships. 



