922 PHYSIOLOGY 



processes into the muscle substance, which dissolve this tissue and then 

 take it up. The absorption of the tail of the tadpole is effected in the 

 same way by means of phagocytes. In mammals, including man, the 

 moulding of the long bone which occurs in the process of growth is 

 effected by continual and coincident processes of absorption and 

 new formation of bone. The absorption is carried out by means of 

 special phagocytes formed by the aggregation of a number of leucocytes, 

 the well-known ' giant cells ' or myeloplaxes which form so prominent 

 a constituent of bone-marrow. 



The blood-corpuscles represent the wandering phagocytes of the 

 body. There are fixed phagocytes of which the myeloplaxes just 

 mentioned may be regarded as a type. Other members of this class 

 are the endothelial cells (Kupfer's ' Sternzellen ') which line the 

 capillaries of the liver. If a suspension of carmine or of micro- 

 organisms be injected into the blood stream these endothelial 

 cells are found a little later to have taken up large numbers of 

 the foreign bodies. Under normal circumstances these 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 

 takes place. These become surrounded with protoplasm and act the 

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

 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 l^>w far the other types of leucocytes which we have 

 described can function as phagocytes. It is probable that the lympho- 

 cytes, and certainly the large mononuclear or hyaline corpuscles, are 

 endowed with these properties. The granular corpuscles, namely, 

 eosinophile and basophile, are thought by some to function as uni- 

 cellular 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 

 unimportant as compared with their role as phagocytes, and are all 

 of them questionable. Thus some authors ascribe to leucocytes an 

 important 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 sub- 

 stances which may act as precursors of the fibrin ferment. In the 



