Pleuro- Pneumonia of Cattle. 201 



«control tubes (tubes 10 and 11), before a reading of the tubes 



-containing the test serum is made. 



If both the antigen and complement controls show complete 

 haemolysis, the serum control tube of each particular serum be- 

 ing tested (tubes 2, 5, and 8) is next examined. If this tube 



.shows complete haemolysis, its companion tube containing antigen 

 is next examined. If the reaction is positive, this antigen tube 



.should show no haemolysis at the time when its serum control 

 tube shows complete haemolysis. If the reaction is negative, 



•complete haemolysis will be shown in the antigen tube as well 



.as in the serum control tube at the same time. 



Border-line reactions sometimes occur, but their number is 

 usually small, and certainly not greater than the number of such 

 reactions obtained with complement fixation tests in other 



•diseases. 



It is important in reading the final result to observe the exact 

 time required for haemolysis to occur in the controls, for, if 

 the reading of. the test is delayed it is possible for a serum to 

 have shown fixation, and the fixation to become masked by a 



subsequent haemolysis. This subsequent haemolysis is due to 



the conglutinin present in the bovine serum, reinforcing the small 



amount of unfixed complement, and assisting that amount of 



complement to haemolyse more or less completely the sensitised 

 red blood cells. This ability of conglutinin to augment the 

 haemolytic power of a dose of complement, too small in itself 

 to produce haemolysis, is strikingly shown in the experiment set 



•out in detail on pages 44-45. 



Results of Complement Fixation Tests. 



Up to the time of writing this report, 63 different bovine sera 

 liave been tested for complement fixation in the manner just 

 •described. Of this number, 14 have given definite positive re- 

 actions, and 47 have given definite negative reactions, while two 

 border line and doubtful reactions have been recorded. 



In each case the reaction given to the test has been checked 

 "by a post-mortem examination of the animal supplying the par- 

 ticular serum tested. 



A number of the animals tested were dairy cows from farms 

 which were quarantined owing to the presence of contagious 

 ^pleuro-pneumonia on them. These animals had each received a 

 prophylactic injection of virus subcutaneously in the tail some 



