292 ILLINOIS STATE DAIRYMEN'S ASSOCIATION 



In addition to these measures adopted to control the spread 

 of the disease, samples of the serum actually used were procured 

 from the owners of the infected herds and also samples of the 

 remaining stock of the Chicago Serum Company. Pigs and 

 calves, the animals which are most susceptible to foot-and-mouth 

 disease, were inoculated with these samples. The results were 

 again negative and after two series of tests had been made, the 

 United States Public Health Service was asked to conduct a third 

 series. This also was negative. 



Up to this time, therefore, four series of tests had been 

 made in which a total of 52 animals had been used. None of 

 these 52 animals developed foot-and-mouth disease and the in- 

 oculations afforded no evidence that the serum was in any way 

 contaminated. Each subsequent series apparently only confirmed 

 the original test made before the serum was permitted to be 

 placed upon the market. The fact remained, however, that herds 

 treated commercially with the serum had developed foot-and- 

 mouth disease. A fifth test therefore was made and ten days 

 after inoculation, the sixty-second animal which had been used 

 in the tests, a calf which had received thirty cubic centimeters, 

 developed characteristic lesions. The diagnosis of foot-and- 

 mouth disease was subsequently confirmed by the inoculation of 

 other animals with material from the infected calf. 



This is regarded as proof that the suspected serum actually 

 was infected. Why the standard tests used on 61 animals fail- 

 ed to reveal this fact is a matter for scientific investigation and 

 the bacteriologists of the Department are now at work upon the 

 problem. At the time of manufacture, one-half of one per cent 

 of carbolic acid was mixed with the serum to act as a preserva- 

 tive. It is now believed that the carbolic acid, acting as a germi- 

 cide, may have attenuated or partially destroyed the virus to 

 such an extent that what have previously been considered safe 

 tests failed to establish the presence of the infection. It is also 

 possible that the virus instead of being disseminated throughout 

 the entire mass of serum, may have become agglutinated. This 

 has been known to occur with germs of other diseases. The re- 

 sult would be the formation in the serum fluid of isolated clumps 



