THE AGGLUTINATION TEST 137 



which are numbered i, 2, 3, 4, 5, 6 in the table on 

 p. 126, were tested at the Brown Institution, and all 

 gave positive reactions in a dilution of from i in 10 to 

 I in 15 ; but it must be remembered that the serum of 

 normal cows will usually agglutinate an emulsion of 

 tubercule bacilli in a dilution of i in 5, or even i in 10 

 (Descos). 



After testing the sera of five normal calves, two 

 normal sheep, and two normal goats, which were all 

 negative, the animals were inoculated with a pure 

 culture of Johne's bacillus (see pp. 150 and 151). Six 

 months later samples of blood were again taken, when 

 it was found that the five calves gave positive results 

 in a dilution of i in 5, whilst the remaining animals 

 showed no trace of an agglutinin. 



Amongst the ordinary laboratory animals the fowl 

 appears to be by far the most suitable for the pro- 

 duction of these antibodies ; but even in this class of 

 animal there is considerable variation as regards the 

 amount of agglutinin obtained. In some cases the 

 serum may agglutinate after a single subcutaneous 

 inoculation in dilutions of i in 20 to i in 40, whilst in 

 others repeated inoculations fail to produce anything 

 like such a strong serum. 



As might be expected, the experiments demon- 

 strated that the agglutination reaction is not specific 

 within the acid-fast group of bacilli. The serum of a 

 tubercular animal will agglutinate an emulsion of 

 Johne's bacillus, and vice versa; the dilution of the 

 serum is, however, usually higher with its homologous 

 bacillus. 



The Complement Fixation Test. — This reaction can 

 also be obtained in the same category of animals as 

 mentioned under the agglutination test ; but it is a 

 more difficult and elaborate test than the latter, and 



