MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 35 



is the lymphocyte, it having been shown by Paton, Goodal, and 

 Gulland that the most marked postprandial increase in leucocytes 

 occurs among the lymphocytes, although there is also increase 

 among the polymiclears. My own researches, as will appear 

 presently, show that the large monocyte is importantly involved, 

 particularly when the parenteral protein to be dealt with includes 

 the full-sized molecule, as frequently happens. 



It is interesting to add that the leucocytic recruits come, ac- 

 cording to Paton and Goodal, not from the intestinal lymphatic 

 tissue, but from the marrow of the bones. Their development 

 is stimulated, we must assume, either (1) directly by food prod- 

 ucts in the blood, or indirectly (2) through the agency of the 

 sympathetic nervous system, or (3) in response to a hormone 

 sent out from the intestine. It is conceivable that the hormone 

 that produces this effect is the secretin of the duodenum, which 

 is known to have a similar stimulating effect on the secretions 

 of the pancreas. 



Pavy developed the hypothesis, which Noel Paton has also 

 advanced, that the leucocytes, after synthesizing the proteins, 

 undergo autolysis, thus discharging their proteins into the blood, 

 to furnish material for the tissue cells. 



It seems probable that there is a measure of truth in the lat- 

 ter part of this hypothesis, referring to the autolysis of the leu- 

 cocyte. In fact, the assumption that autolysis occurs seems 

 unavoidable, in view of the observed rapid fluctuations in the 

 leucocytic population even in health. But it is highly improb- 

 able that the leucocyte (in its mature state) synthesizes pro- 

 tein ; or that the main function of handling protein-products of 

 the intestine is dependent upon the leucocyte. As to this, Halli- 

 burton's suggestion, to the effect that the number of leucocytes 

 in the blood stream is inadequate to perform this function in its 

 entirety, seems fairly conclusive. Halliburton argues that the 

 total blood stream contains only about one gram of lymphocytes ; 

 and even if this amount were doubled during digestion, "it is 

 difficult to see how two grams of lymphocytes can tackle the 

 enormous burden which every meal must put upon them." It 

 should be observed, however, that the quantity of foreign protein 

 in the blood at any one time is small. But the aggregate quantity 

 of serum protein is, of course, relatively enormous, and in the 

 last analysis it is clear that this is the product of the synthesis 

 of food proteins. 



According to the present view, the leucocytes are not called 

 upon to "tackle" this problem, which is handled effectively by 

 the mother cells that generate leucocytes and red corpuscles, 

 notably the latter. These mother cells (in bone marrow, spleen, 

 and in case of certain leucocytes lymphatics) synthesize protein 



