Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/81

 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 0.1 gr. of ammonium oxalate is added to the test-tube containing the blood, so as to prevent it from clotting. The form-elements are centrifuged out, and the clear plasma can then be withdrawn easily by means of a pipette.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 hæmoglobin, for, if it is present, then the red blood corpuscles 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 hæmoglobin must be used for these experiments. To a measured quantity of serum or plasma a certain quantity, in cubic centimetres, of