56 FORMATION OF DEFENSIVE FERMENTS 



and particularly with the body, find their way into 

 the plasma of an organism by any other way than 

 through the intestinal canal. The order of these 

 experiments was of the following character :- 



In the first place we determined the composition of 

 the blood plasma, or of the serum, in an animal, in 

 regard to the proteolytic and peptolytic ferments it 

 contained under normal conditions, that is to say, 

 when the nourishment is normal. The manner in 

 which this is done is as follows : 10 c.c. of blood is 

 taken from the animal under experiment, for instance, 

 from a dog, from the vena jugularis externa or from 

 a vein of the leg. Either this is left to clot of its own 

 accord, so as to separate out the serum ; or else o'i gr. 

 of ammonium oxalate is added to the test-tube con- 

 taining the blood, so as to prevent it from clotting. 

 The form-elements are centrifu^ed out, and the 



o 



clear plasma can then be withdrawn easily by 

 means of a pipette. In both cases serum and 

 plasma we must test for the absence of haemo- 

 globin, for, if it is present, then the red blood cor- 

 puscles have been broken up, in which case we may be 

 quite certain that the ferments belonging to the red 

 corpuscles have passed into the fluid derived from 

 the blood. Only serum and plasma which are 

 absolutely free from hemoglobin must be used for 

 these experiments. To a measured quantity of serum 

 or plasma a certain quantity, in cubic centimetres, of 



