312 INFECTION AND IMMUNITY 



heritage of their free-swimming ancestors, and that they have not 

 suffered the total specialization and physiologic degeneracy of the fixed 

 tissue cells, seems sufficient evidence to warrant the conclusion that 

 they are most active factors in the protection of the specialized internal 

 tissue cells, which control the general metabolism and higher func- 

 tions of the animal body. It seems worth mentioning that the 

 leucocytes, alone probably of all the true cells of the body, are entirely 

 independent of the nerve control, and are subject only to the stimula- 

 tion of their chemical and physical environment, and are thus sus- 

 ceptible 'of adaptation to and capable of subserving various purposes 

 which would be fatal to the duties of cells controlled by the nerve 

 mechanism for the special functions of the organism at large. Further 

 than this the death of leucocytes does not matter, as would the death of 

 specialized and nerve-controlled cells, for no special metabolic or func- 

 tional derangement occurs from their destruction. 



In considering this independence of the leucocytes it must not be 

 assumed that they have not varied from primitive ameboid cells, for un- 

 doubtedly their life and proper functioning are largely determined by the 

 special plasma in which they live, and it may be that their food, although 

 at times crude compared with that of the other body cells, is never- 

 theless usually prepared for them by processes going on in the plasma. 



Questions relating to the independence and to the interrelation of 

 the plasma and leucocytes in their action on invading microorganisms 

 and the action of plasma as compared with serum have been ground for 

 scientific strife for many years, one side contending for the activity of 

 the plasma, the other for the activity of the phagocytes; the humoralist 

 at first neglecting, if not absolutely forgetting, that' a fluid can not be 

 self-replenishing, while the supporters of phagocytosis largely over- 

 looked the fact that plasma is not necessarily an inert menstruum such 

 as salt solution. 



While these differences have been to some extent adjusted by the 

 theory and work of Ehrlich, an immediate point of contention is still the 

 question of the similarity of action of plasma and serum. The humoral 

 school contends that the alexin of Buchner complement of later 

 writers is secreted into the plasma, while the Metchnikoff school 

 claims that it is only given up from injured leucocytes in the body, 

 and to the serum by destruction of leucocytes during coagulation. The 

 Metchnikoff school maintains, however, that the amboceptors necessary 

 for bactericidal and bacteriolytic action are formed in excess in the 

 phagocytes, and given off from these to the plasma, yet asserts that 



