252 'MISSOURI AGRICULTURAL REPORT. 



saves the life of your child, when it may be necessary to inject enough 

 antitoxin into that child which would neutralize enough poison to kill 

 300,000 guinea pigs. The child may contain much more poison than 

 would be required to kill 300,000 guinea pigs. How could you expect 

 it to live unless you could succeed in destroying this poison? This you 

 can do with antitoxin, and this alone. 



Now we will discuss vaccine. You are all aware that human beings 

 do not contract certain diseases which attack your stock. These human 

 beings are said to be naturally immune to those diseases which they do 

 not contract even when exposed to them. You are also aware that a 

 certain number of men may be exposed to an infectious disease, some 

 may contract that disease while others escape. Thus several men may 

 drink water containing typhoid germs, only a few of them may con- 

 tract the disease. Now those who do not contract the typhoid fever may 

 escape because they are immune to that disease. There are various ways 

 in which we can explain this immunity but we will not discuss that here. 



I have previously stated that when an individual recovers from an 

 infectious disease unaided by a physician, it is because his system has 

 built up in it something by means of which it protects itself from the 

 harmful effects of the poison of that disease. After recovery this some- 

 thing which saved him from the harmful effects of the poison of the dis- 

 ease remains in his system for a long time. It may remain in his system 

 for a life time or only a few months. If it remains in his system for a 

 life time he will not again contract the same disease, if it remains there 

 only a short time he may contract the same disease when exposed again. 

 We find different conditions in different diseases and have to explain this 

 immunity in different ways, but this is the general law. An immunity 

 acquired by having had the disease is known as "acquired immunity." 

 You all know that when one has once had smallpox he is not liable to have 

 it again, because his system has built up in it something which renders 

 the poison of smallpox harmless, and hence the cause of smallpox can in 

 no way harm the body again. 



Before going further I wish to say that the immunity of the body 

 in general is greatly influenced by the care we take of our bodies. Thus 

 a man exposes himself to rain and cold and then contracts pneumonia. 

 The rain and cold lowers the resistance of his body and then the germ 

 of pneumonia takes hold and immediately begins to manufacture its 

 poisons. The same thing applies to the proper feeding and exercise of the 

 body, as is well shown in animal experiments. 



We all know that epidemics of diseases vary in virulence from 

 time to time. We also know that when a disease first gets a foothold 

 in a country it gradually increases in virulence. We find by experiments 



