t66 ^nssouRi agricultural report. 



This has been observed for a long- time, and is known as natural im- 

 munity. Some scientific people came to the conclusion that they 

 could produce a disease in an animal, establish immunity thereby, but 

 not produce the disease in such a form as would kill the animal, and 

 in that way save a great many head of stock. That theory is worked 

 out until now we use vaccine commercially for blackleg, anthrax, etc. 

 There is a theory or hypothesis on which all this is based, and I want 

 to explain it briefly so that I can point out something of the danger 

 in its use. 



The theory is that when some pathologic organisms once enter 

 the system they commence to multiply and elaborate a poison known 

 as toxin, which is carried to the various parts of the animal body 

 through the circulatory system and produces what we know as dis- 

 ease. The poison from the various different pathogenic organisms 

 ]-roduces a different series of S5'mptoms which we recognize as specific 

 disease. If this production of toxin-poisoning went on indefinitely 

 the result would be the death of the individual, but nature has pro- 

 vided a means to hold this in check. There is thought to be produced 

 a material which we choose to call anti-toxin whenever there is a 

 disease caused by the presence in the animal body of certain organ- 

 isms. The disease is counteracted by this substance known as anti- 

 toxin, and we make use of this anti-toxin in various ways. The one 

 disease in which we have come to use it commercially is that of 

 tetanus or lock-jaw. 



In some cases anti-toxin for tetanus is proving very efficient, 

 while in others it is not, and the reason we attribute to this difference 

 in results is that after the disease has gone so far that the poison has 

 entered the different organs and has made certain anatomical changes, 

 we know there is no agent that we can introduce into the system that 

 will check the disease; whereas, if the anti-toxin is injected into the 

 system previous to the poison's once reaching the center, it is going 

 to work and it will neutralize the poison and the animal may recover. 



In vaccination, as you know, we introduce into the animal or- 

 ganism a deadly germ and this germ has been so treated, i. e.. has 

 ]:'assed through certain environments, certain uncongenial conditions, 

 such that it will not produce the disease in its original vigor. But at 

 tlie same time it will produce some toxin, and this encourages the 

 animal system to produce the anti-toxin or neutralizing agent, and 

 from this the animal becomes immune and resists any subsequent 

 .attack of the disease. 



You sec. if we can b\- l<ccping these germs under unfavorable con- 



