FERMENTATION . 229 



guinea-pig (one that has not been injected with 

 rabbit blood). 



In a few minutes the mixture becomes limpid 

 and red. The laking power is restored. 



Obviously, with the fresh serum was added 

 the unstable body destructive to red corpuscles. 

 Ehrlich and Morgenroth have shown that at low 

 temperatures the stable body unites with the red 

 corpuscles while the unstable body remains in 

 the serum ; in this case the haemoglobin is not 

 set free. At higher temperatures the haemoglo- 

 bin separates and the unstable body is found to 

 have left the serum. It has joined the stable 

 body in the sediment. 



Following the side-chain theory already men- 

 tioned, fihrlich and Morgenroth assume that the 

 stable substance has two combining powers; 

 on the one hand it unites with the red corpus- 

 cles, on the other with the unstable substance, 

 thus bringing it to the cell which it may then 

 destroy. 



Immunity against toxines and foreign red cor- 

 puscles are only two of the protective actions of 

 the blood. The injection of cells of the most 

 varied kinds is followed by the production of 

 specific protective bodies; 1 thus, the injection of 



1 Metchnikoff: Annales de 1'Institut Pasteur, 1900, xiv, 

 p. 369. 



