274 Annual Report for 1912 of Royal Veterinary College. 



a suspected animal, and if agglutinin has been present in this 

 serum the effect of the addition is to cause the hazy liquid to 

 become clear. This clearing up of the liquid is ascribable to the 

 fact that the agglutinin acts on the suspended bacilli and 

 causes them to collect together in clumps, which then tend to 

 fall to the bottom of the tube. 



The quickness with which this effect is produced depends 

 on a number of different factors, including the amount of serum 

 added and the temperature at which the experiment is carried 

 out. It may be said, however, that when any considerable 

 amount of agglutinin is present in the animal's blood the effect 

 of the test is very striking when one compares the appearance of 

 a control tube of bacterial mixture without serum with that 

 of a tube of the same mixture to which serum has been added. 

 In the former tube the mixture preserves all its original 

 haziness, while in the latter it may have become as clear as 

 pure water. 



In order to appreciate the actual value of the agglutination 

 test for the diagnosis of any disease one must know (1) whether 

 the test generally or always has a positive result when serum 

 from a diseased animal is used, and (2) whether a similar 

 positive result is ever or frequently obtainable with serum from 

 a healthy animal, or from one not affected with that particular 

 disease. It is obvious that a test which frequently failed to 

 give positive results with serum from a diseased animal would 

 not be of great value, and that a test which frequently gave 

 positive results with serum from healthy animals would be 

 quite useless. 



It was therefore resolved to make a large num1)er of com- 

 parative observations, using blood both from presumably 

 healthy animals and from others which had actually aborted 

 or which belonged to herds in which one or more cases of 

 abortion had recently occurred. The first class of animals 

 included 535 bulls, steers, non-pregnant heifers, and young 

 calves, and it was found that in only one of these animals was 

 the result of the agglutination test markedly positive. Among 

 127 animals which had recentl^^ aborted or which came from 

 herds in which cases of abortion had recently occurred the test 

 had a positive result in sixty-two cases. Up to the present time 

 there has not been encountered any case certainly known to be 

 one of contagious abortion in which the animal's blood has not 

 reacted positively to this test. It ought to be stated, however, 

 that in one instance the blood of a cow which had recently 

 aborted failed to give a positive result with the agglutination 

 test, although the circumstances rather strongly indicated that 

 the abortion had been of the contagious kind. However, even 

 allowing that this was a case of actual failure of the test, and 



