THE PROTEOLYTIC MECHANISM IN OPERATION 93 



produced, partly at least, by the red corpuscles in response to 

 bacterial toxins. But in general it is probably the leucocyte, 

 with its less specialized organization, that aids the red corpuscles, 

 rather than the converse. 



As a typical instance, we may note that whenever the red 

 corpuscles are decreased in number say from vigorous blood- 

 letting the army of leucocytes at once receives notable acces- 

 sions, being fully replenished within a few hours. A far longer 

 time will be required to replace the vast coteries of red cor- 

 puscles; meanwhile it is the part of wisdom to strengthen the 

 leucocytic outposts. In some cases the numbers of leucocytes 

 may become so great that their bodies must have a really sig- 

 nificant share in replenishing the proteins of the blood stream, 

 thus making partial amends in this direction also for the paucity 

 of red corpuscles. 



THE LEUCOCYTIC BALANCE 



The consideration of such fluctuations in the ranks of the cor- 

 puscles naturally raises a question as to how the leucocytic bal- 

 ance is maintained. 



We know that under average conditions of normal health the 

 number of leucocytes in the blood stream averages about six 

 thousand to the cubic millimeter, rising to about eight thousand 

 three or four hours after a hearty meal ; and that the number 

 of red corpuscles averages about five million to the cubic mil- 

 limeter and is less subject to wide variations in times of health. 



These facts are so familiar that we scarcely think of them 

 as requiring explanation. Yet a moment's consideration makes 

 it clear that the maintenance of the corpuscular balance is a 

 very puzzling phenomenon. 



How are the mother cells in the bone marrow and spleen, for 

 example, to know that protein foods have been taken into the 

 stomach, and that therefore an additional supply of leucocytes is 

 needed? How are these mother cells to know that there has 

 been a great destruction of red corpuscles in the liver; or that 

 a wound in some remote part of the body has resulted in a 

 severe hemorrhage? How are they to know that a colony of 

 pneumococci has found lodgment in the lungs, and that fresh 

 bands of phagocytes are required to fight them? How are they 

 even to know that the body is undergoing vigorous muscular exer- 

 cise; or that a cold bath has been applied to the skin? 



These surely are interesting questions. Under all the condi- 

 tions just noted, the cytogenic cells do, in point of fact, take on 

 exceptional activity, and produce leucocytes in particular in un- 

 wonted numbers. 



