Pleuro- Pneumonia of Cattle. 193 



stance," but which they afterwards termed " conglutinin." The 

 name " conglutinin "« was suggested by the action of this sub- 

 stance upon sensitised red blood cells, with a suitable comple- 

 ment. In such a combination the red blood cells were ener- 

 getically " agglutinated " and sedimented. Although the reac- 

 tion was similar to the action of a powerful agglutinin, it differed 

 from the action of an agglutinin in that complement was a neces- 

 sary ingredient in the combination for this phenomenon to occur. 

 Complement is not necessary to complete the action of an agglu- 

 tinin. 



These authors found that this substance — conglutinin — pre- 

 sent in varying amounts in bovine sera, was capable of exer- 

 cising a remarkable influence upon the final result in a haemolytic 

 test. In a series of experiments they demonstrated that the sub- 

 stance, acting in conjunction with a weak complement, could con- 

 glutinate and haemolyse sensitised red blood cells, although the 

 amount of complement taking part in the reaction, by itself and 

 without conglutinin, was incapable of producing haemolysis. In 

 other words, it was demonstrated that conglutinin could com- 

 bine with a weak complement, and the combination could then 

 exert a powerful haemolytic action upon sensitised red blood 

 cells. 



In the technique of the complement fixation tests described in 

 the previous chapter, the complement was titrated against one 

 unit of sensitised red blood cell suspension, in order to deter- 

 mine the minimum haemolytic dose (M.H.D.) of complement. 

 Against this standardised haemolytic system the other ingredi- 

 ents of the test were titrated, in order to ascertain the proper 

 quantities of each to employ in the final stage of the test. When, 

 however, in the final test, bovine serum and complement are 

 mixed together, and incubated, and then sensitised red blood 

 cells are added, the influence of conglutinin becomes exerted, and 

 the previously titrated M.H.D. of complement apparently be- 

 comes more than the M.H.D. required for haemolysis, so that 

 a fixation with a positive serum may still leave sufficient, com- 

 plement available to be reinforced by the conglutinin present, 

 and produce haemolysis of the sensitised red blood cells. 



In order to test this hypothesis, the following experiment was 

 carried out: — 



A series of tubes (Series A) was set up, and into each tube 

 was measured decreasing quantities of fresh guinea-pig's serum 

 (1 in 10 dilution), from 0.5 c.c. downwards. The fluid in all 



