298 THE ROLE OF AGGLUTINATION IN IMMUNITY, 



The experiments showed that the race of bacterium had no 

 influence: all races are phagocytosed after agglutination. In 

 washing the agglutinated bacteria, there are always a number of 

 cells that remain suspended in the normal saline after centrifuging 

 in the hand-centrifuge (h?ematocrit, Beck). They are undoubtedly 

 free cells broken away from the clumps, and though they refuse 

 to sediment readily, they are still covered with the agglutinated 

 substance. A similar refusal to sediment could be obtained by 

 triturating a flocculated precipitate with a saline solution of the 

 same densit}'^ and composition as that in which the flocculation 

 was induced. Experiment 3 shows the effect of the opsonins of 

 normal serum upon the bacteria and their destruction by heat. 



The confirmation of previous results. — A small quantity of 

 active serum was obtained from a fresh case, that of a boy who 

 had been ill for nine or ten days. The limit of agglutination 

 was 1 : 100; the tubes being maintained at 37° for 30 minutes. 

 After being heated at 60° for 15 minutes, the limit of aggluti- 

 nation had sunk to 1:10. The ratio 1:12-5 was doubtful, 

 and ratios of 1 to 20, 33, 50 and 100 showed no agglutination. 

 The tubes containing the tests were gently centrifuged (2000 

 revolutions per minute for three minutes) and a sedimentation 

 was noted in all of those containing the heated serum. The 

 precipitate became smaller and smaller as the dilution became 

 greater. This behaviour is in sharp distinction to that of the 

 unheated serum, which, under the same treatment, shows a 

 sedimentation in those tubes only that exhibit agglutination. 

 The same phenomenon was observed in the active serum 

 previously examined. It would appear that Dreyer's contention 

 is correct and that centrifuging accelerated the reaction which 

 had been slowed by the exposure to 60°. 



In the following experiment the bacteria, agglutinated by 

 unheated serum in a dilution of 1 : 100, were tested against those 

 agglutinated by the heated serum of which all the precipitates 

 were collected and washed. 



Serum unheated. 1:100.. ... ... ... Phagocytosis. 



Serum heated ... ... ... ... ... , , 



Control (no serum)... ... .. ... ... No phagocytosis. 



