20 BOARD OF AGRICULTURE. 



time and skill in the preparation and use of the virus, and 

 this deteriorates so rapidly that it must be used when quite 

 fresh or its results are not satisfactory. Again, this modi- 

 fied virus penetrates too deeply, and sometimes produce* 

 more extensive local inflammation, and secures a less degree 

 of immunity, than is desirable. In some cases, too, it i& 

 unsafe to the operator. The methods with heat and disin- 

 fectants do not require so much skill, but the other objec- 

 tions apply to them as well. But no method of attenuation 

 yet discovered is sufficiently simple to be practised by the 

 ordinary farmer or stock-raiser, and, consequently, if any 

 practical benefit is to be derived from these discoveries, the 

 vaccine must be prepared at a central point and distributed 

 broadcast over the country. And when we attempt this we 

 are confronted by difficulties too serious to be overlooked. 

 It would be very wrong to thus distribute a virus danger- 

 ous to human life, like the anthrax virus, and this is almost 

 the only one in which the prepared vaccine retains its activ- 

 ity a sufficient time to be sent to any considerable dis- 

 tance. Even the germ of this disease, which, from its pecu- 

 liarity of forming spores or seeds, is the most stable of all 

 viruses, rapidly becomes inert and useless after it has been 

 subjected to the attenuating process. 



The stronger and more active a virus is, the longer it is 

 able to resist unfavorable conditions of life without beinsr 

 modified by them ; and, consequently, if we were distribut- 

 ing virus to use at a distance it would be an object to send 

 it in the most virulent condition possible. With this fact in 

 view I commenced, several years ago, a series of experiments 

 with diluted virus in the hopes of obtaining a method of pro- 

 ducing immunity free from the chief objections which are 

 urged against the methods I have mentioned. It is a ques- 

 tion which many of the ablest experimenters had attempted 

 to solve, but it had been abandoned again and again, and no 

 very definite results had been obtained. The great trouble 

 seemed to be that they worked with virus which varied enor- 

 mously in strength. We can understand this when we exam- 

 ine the blood of a number of animals which have died of 

 anthrax, for example. In one case we may find twenty, 

 thirty, forty bacilli, even, in a single microscopic field, which 



