382 ADVANCED PHYSIOLOGY 



body (probably those of the blood vessels in particular) being 

 irritated by these toxins, endeavor to defend themselves by 

 giving off materials which nullify the poisons. These sub- 

 stances are called antitoxins. If the body cells can create 

 sufficient antitoxin rapidly enough, the bacteria as well as their 

 products are overcome, and the person will soon be well again. 

 It is quite obvious that the blood of a person so recovering 

 contains antitoxin substances which will make him safe from 

 similar attack so long as they last. He is then said to be 

 actively immune to that special disease. 



One may secure immunity against some diseases by means 

 other than first going through a period of sickness with it. 

 The commoner means are by vaccination and by serum 

 inoculations or injections. The principle on which both these 

 procedures work is this: if, instead of virile disease bacteria, 

 very weak (attenuated) germs, or the toxin secreted by them, 

 are introduced into the human body through a shallow abrasure 

 or cut in the skin (vaccination) or by hypodermic injection 

 (injection or innoculation) , enough antitoxin is immediately 

 produced by the body so that the weak germs are killed off 

 and the toxin made of no effect. With antitoxin thus on 

 hand, the body has a "running start" and can successfully 

 compete against the invasions of strong, vicious bacteria of 

 the same sort. This is the manner of procedure against 

 typhoid and small-pox. The wide use of vaccination for 

 small-pox and innoculation for typhoid fever has thoroughly 

 established their reliability and safety. Persons so rendered 

 safe from a certain disease are said to be artificially immune. 



Instead of injecting weak and dying bacteria or the toxin 

 characteristic of them, the body can be fortified against some 

 diseases by injecting antitoxin taken from some animal which 

 has had the disease and recovered from it; this is the case 

 when serums are injected to ward off diphtheria. Curiously 

 enough, the body cells can be deceived in this way, and on 

 becoming "conscious" of the presence of some antitoxin will 



