450 



COLLECTED STUDIES IN IMMUNITY. 



pig blood solutions this is very simple, for on strongly centrifuging 

 the solution used for complementing, especially if some salt is added, 

 the stromata settle out very well. By removing the supernatant 

 haemoglobin solution and perhaps once more washing the sediment, 

 the stromata are readily isolated. This suspension of blood stromata, 

 made up to the original volume with salt solution, showed itself 

 just as capable of activating cobra venom as was the original blood 

 solution, whereas the decanted fluid was entirely inert. The activating 

 substance of the blood solution is present therefore not in solution but 

 as a constituent of the stroma of the blood-cells. (See Table VII.) 



TABLE VI. 



TABLE VII. 



Amounts of 



Ox Blood + 01 cc. 1% Cobra Venom + 



This threw some light on the inactivation of the blood solution at 

 62 C., a fact which made the complement character of the acti- 

 vating substance seem exceedingly probable. In contrast to the 

 native blood solution we find that the suspension of stromata remains 

 unchanged when heated to 62 C. 



