CHAPTEE XII 



THE QUESTION OF IMMUNITY AND ANTITOXINS 



Bacterial Products — Toxins — Question of Immunity — Kinds of Immunity — Theories 

 of Immunity — Applications of Immunity — Vaccination for Small-pox : Effect 

 of Vaccination — Pasteur's Treatment for Rabies — Inoculations for Cholera, 

 Typhoid, and Plague — Antitoxin Treatment of Diphtheria and its Effects. 



The term natural immunity is used to denote natural resistance to 

 some particular specific disease. It may be due to species of animal, 

 or age, or individual idiosyncrasies. We not infrequently meet with 

 examples of this freedom from disease. Certain species of animals 

 do not, as a rule, take certain diseases. For example, cholera and 

 typhoid, which affect man, do not affect the lower animals. Swine 

 plague, which affects swine, does not affect man. The white rat 

 is immune to anthrax, which readily attacks cattle. Such examples 

 might easily he multiplied. Children, again, are susceptible to 

 certain diseases and insusceptible to certain others to which older 

 people are susceptible. The young of the lower animals also are 

 susceptible to diseases which do not attack adult animals. We 

 know, too, that some individuals have a marked protection against 

 certain diseases. Some persons coming in the way of infection at 

 once fall victims to the disease, whilst others appear to be proof 

 against it. 



It is only in recent times that any intelligent explanations have 

 been offered to account for these phenomena. The most recent, and 

 that which appears to have most to substantiate it, is known as 

 immunity due to antitoxins. To understand the nature of antitoxins 

 it is necessary to consider briefly the products of bacterial activity. 

 They are chiefly seven : — 



