66 
As a further proof that the blood serum of an immunized guinea 
pig can not ^transfer this immunity, we added such serum from sev- 
eral guinea pigs immunized by repeated injections with normal horse 
serum; but when this mixture is injected into susceptible pigs they 
react in a characteristic manner. The experimental data upon this 
point will be seen in Part IV, page 37, upon the relation of precipitin 
to the toxic action. 
It therefore appears that the “immune bodies,’’ if such exist 
against the toxic action of horse serum, are not free in the blood and 
body juices, contrary to the case in diphtheria. 
