VETERINARY PROBLEMS. 21 



means that there are two millions or more in every drop ; in 

 another case we may find but two or three bacilli, and con- 

 sequently there are scarcely a tenth as many as in the former 

 case. In still another case it is difficult to find them at all. 

 Now it is very evident that if we diluted each kind of blood 

 with say twenty-five thousand times its bulk of water and 

 wsed a drop of the mixture for inoculation, the first animal 

 operated upon would receive into its body at least one hun- 

 dred bacilli, the second not more than ten, and the third 

 might escape without a single one. What wonder, then, that 

 dilution experiments, made with blood in which the number 

 of germs was never even estimated, should produce uncer- 

 tain and confusing results. 



The methods of cultivating such gei:ms outside of the body, 

 which reached great perfection during the investigations 

 which were necessary to prove that certain diseases were 

 caused by these germs, enabled us to take a step in advance 

 of those who had previously studied this question. Each 

 germ, we reasoned, must require a certain amount of food for 

 its development, and, consequently, if the cultivation broth 

 was always made of a certain strength and the germs were 

 allowed to grow until they had exhausted the nutriment, there 

 ought to be a practically constant number in every drop of 

 every cultivation made under such conditions. And this 

 proved to be true, and for years we have been able to pro- 

 duce at will a virus of fowl cholera which contained, as 

 nearly as could be estimated, two and a quarter millions of 

 germs in every drop. Even this did not produce exactly 

 uniform results, because some birds were much more sus" 

 ceptible than others, but it enabled us to demonstrate some 

 very important and interesting facts. 



When the virus was diluted with five hundred or a thou- 

 sand times its bulk of a harmless liquid it was noticed that a 

 less number of the inoculated birds sickened than was the 

 case when the strongest virus was used, while the disease 

 when produced was as severe as before. When the dilution 

 reached five thousand or ten thousand times, a still smaller 

 number sickened and the attack was not less fatal than be- 

 fore. It was such results as these that had puzzled other 

 investigators and led them to conclude that their dilutions 



