-■386 H. R Seddon .- 



therefore, as if there were at least two maxima of agglutination, 

 for a given quantity of serum, varying with the quantity of emul- 

 :«ion, and, between these two maxima, the zone of inhibition. 



A peculiar agglutination phenomenon similar to this had been 

 noted before with serum from the same animal. 



In this previous test the same amount of emulsion was used in 

 «ach tube, and the following quantities of serum Avas placed in 

 tubes : — 



Tube. A. B. C. D. E. I-'. G. 



0.15 - 0.1 - 0.075 - 0.05 - 0.02 - O.ol - 0.005 c.c, 

 Resiilt - +- + - + -++-++-- 



After incubation for 24 hours, there was agglutination deposit 

 in all the tubes except G, but there was a marked increase of 

 •opacity of the supernatant fluid going from C. to A — i.e., with the 

 greater amount of serum. The only tubes where the super- 

 natant fluid cleared were D and E. After incubating 

 for a total of four days, all the tubes — A, B and C — 

 showed clearing. Emulsion controls, it should be noted, 

 remained unchanged---^.e., were not sedimented. It was considered 

 at the time that, as the most outstanding feature was the failure 

 of A, B and C to sediment, the cause might be physi- 

 cal, and that the reason sedimentation did not occur was 

 because of the increased viscosity in these tubes, due to 

 the large amount of serum. In view of the further ex- 

 periment detailed above in Table 2, and of the mention by Hew- 

 lett of a similar phenomenon of a zone of inhibition with M. Meli- 

 fensis, no suggestion as to the cause is offered. No op})ortunity 

 of consulting the work referred to by HeAvlett has been possible, but 

 the phenomenon, in the main, seems parallel. 



The phenomenon is of importance in that an apparent falling off 

 in the agglutinating power of a serum does not necessarily mean 

 that the end-point is to be expected in the next tube. 



There may be a zone of lessened agglutination, and then a fur- 

 ther increase may be met before the end-point of agglutination re- 

 action. This "end-point" of reaction figure is important in 

 Contagious Abortion, as it affords a means of comparing an ani- 

 mal's condition from time to time as regards the progress of the 

 •disease. 



c. — Ojitimum Amount of Eniuhion to V xe . 



Having determined the points referred to earlier in this paper, 

 ■the question of optimum quantity of bacterial emulsion naturally 

 arises. 



