204 ESSENTIALS OF VETERINARY LAW 



in the case of serum supplied by many states. It 

 is well to use serum from two or more lots at the 

 same time, and when this is practiced they should 

 not be used indiscriminately. When so used it 

 would be practically impossible to trace the in- 

 fection should harm result. On the other hand, 

 a ' * control ' ' test may offer efficient aid. For exam- 

 ple: Suppose a veterinarian has lots of X and Y 

 serum, enough to treat herds of A. and B. If he 

 used the lots of serum indiscriminately, and 

 disease broke out soon after, there would be little 

 to show that the disease was due to the use of 

 either lot. If X were used only on the A herd, 

 and Y on the B hogs, the occurrence of foot and 

 mouth disease in the A herd would point to the X 

 serum as a possible source. But if X were used 

 on the A herd except two or three animals, on 

 which Y was used; and Y were used on the B herd, 

 except a few on which X were used; then if the 

 disease occurred only among the A herd, irrespect- 

 ive of the serum used, it would indicate that the 

 disease was not due to the serum ; but if it showed 

 first in the X animals of each herd it would be 

 strong* evidence of infection in the X serum. In 

 such use of two lots the exceptional animals in 

 each herd must be clearly and surely indicated in 

 the record. 



If in addition the veterinarian made a practice 

 of reserving one package from each lot used, for 

 a period of from fifteen to thirty days, there would 

 be a possibility of surely demonstrating the qual- 

 ity of the article. There is another, and a selfish 

 reason for the veterinarian adopting this practice. 

 If after the use of serum, septicaemia breaks out 



