860 PHYSIOLOGY 



cells, as well as some similar cells in the spleen, take up effete red blood 

 corpuscles and destroy them. During the process of degeneration of a 

 peripheral nerve brought about by its separation from the ganglion cells 

 of which its fibres are the processes, a marked proliferation of the nerve 

 nuclei occurs. These become surrounded with protoplasm and act 

 the part of phagocytes, loading themselves with the fat globules set iree 

 by the degeneration of the myelin sheath. To the same class of fixed 

 phagocytes may possibly be ascribed certain of the plasma cells of the 

 connective tissues. 



That the polymorphonuclear leucocytes are endowed with these 

 phagocytic properties is universally acknowledged, but some doubt still 

 exists as to now far the other types of leucocytes, which we have described, 

 can function as phagocytes. It is probable that the lymphocytes, and 

 certainly the large mononuclear or hyaline corpuscles, are endowed with 

 these properties. The granular corpuscles, namely, eosinophile and baso- 

 phile, are. thought by some to function as unicellular glands and to react 

 to infection, not by englobing the micro-organisms, but by discharging 

 substances stored up in their granules which have a poisonous effect on 

 the micro-organisms, and so prepare them for subsequent ingestion by the 

 polymorphonuclear leucocytes. 



The other functions, which have been ascribed to leucocytes, are un- 

 important as compared with their rdle as phagocytes, and are all of them 

 questionable. Thus some authors ascribe to leucocytes a significant 

 part in the taking up of fat from the intestine and its carriage into the 

 lymphatic system. In the coagulation of the blood the leucocytes have 

 been supposed to act by the discharge of substances which may be 

 precursors of the fibrin ferment. In the invertebrata the wandering 

 mesoderm cells not only remove the injured tissue but apparently give 

 rise to new connective tissues. The same function was formerly assigned 

 to the leucocytes of mammals by Ziegler; and MetchnikofE believed 

 that, after the removal of any injured tissue, the emigrated leucocytes 

 undergo elongation to form so-called fibroblasts, by the further division 

 of which are produced the white fibres of the connective tissues as well as 

 the branched connective-tissue cells. Most authors at the present time 

 have come to the conclusion that the work of the leucocytes is complete 

 with the removal of dead or injured tissue, and that the process of regenera- 

 tion is carried out by the plasma cells of the connective tissue, which enlarge, 

 undergo division, and form the fibroblasts of the developing tissue. These 

 plasma cells can change their position and act as phagocytes, eating up 

 and digesting the polymorphonuclear leucocytes which have prepared 

 the way for their regenerative activity. Their amoeboid power is shown 

 by the fact that if two sterile cover glasses be introduced under the skin, 

 new connective tissue is formed between the cover glasses ; and this method 

 has been adopted by Ziegler for the study of the cellular changes involved 

 in the regeneration of this tissue. 



