BLOOD. 49 



described. (5) They help to maintain the normal composition of the blood- 

 plasma as to its proteids. It may be said for this view that there is considerable 

 evidence to show that the leucocytes normally undergo disintegration and dis- 

 solution in the circulating blood, to some extent at least. The blood-proteids 

 are peculiar, and they are not formed directly from the digested food. It is 

 possible that the leucocytes, which are the only typical cells in the blood, aid 

 in keeping up the normal supply of proteids. From this standpoint they 

 might be regarded in fact as unicellular glands, the products of their metab- 

 olism serving to maintain the normal composition of the blood-plasma. 

 The formation of granules within the substance of the eosinophiles offers a 

 suggestive analogy to the accumulation of zymogen granules in glandular 

 cells. As to the origin of the leucocytes, it is known that they increase in 

 number while in the circulation, undergoing multiplication by karyokinesis ; 

 but the greater number are probably produced in the lymph-glands and in 

 the lymphoid tissue of the body, whence they get into the lymph-stream and 

 eventually are brought into the blood. 



Physiology of the Blood-plates. — The blood-plates are small circular 

 or elliptical bodies, nearly homogeneous in structure and variable in size (0.5 to 

 5.5//), but they are always smaller than the red corpuscles (see Histology). Less 

 is known of their origin, fate, and functions than in the case of the leucocytes. 

 It is certain that they are not independent cells, and it is altogether probable, 

 therefore, that they soon disintegrate and dissolve in the plasma. When 

 removed from the circulating blood they are known to disintegrate very 

 rapidly. This peculiarity, in fact, prevented them from being discovered for 

 a long time after the blood had been studied microscopically. Recent work 

 has shown that they are formed elements, and not simply precipitates from the 

 plasma, as was suggested at one time. The theory of Hayem, their real 

 discoverer, that they develop into red corpuscles may also be considered as 

 erroneous. There is considerable evidence to show that in shed blood they 

 take part in the process of coagulation. The nature of this evidence will be 

 described later. 



Lilienfeld 1 has claimed that chemically the blood-plates contain a nucleo- 

 albumin (see section on Chemistry of the Body), to which he gives the specific 

 name of "nucleohiston." The same substance is contained in the nuclei of 

 leucocytes. This latter fact may be taken as additional evidence for a view 

 which has already been supported on morphological grounds — that the blood- 

 plates are derived from the nuclei of the leucocytes. According to this 

 theory when the polynuclear leucocytes go to pieces in the blood the frag- 

 ments of nuclei contained in them persist for a longer or shorter time as 

 blood-plates, that in time eventually dissolve in the plasma. If this last 

 statement is correct, then it follows that the substance contained in the blood- 

 plates either goes to form one of the normal constituents of the plasma, useful 

 in nutrition or otherwise, or that it forms a waste product that is eliminated 

 from the body. 



1 Da Bois-lleymond's Archiv fiir Physiologic, 1893, S. 5G0. 

 Vol. I.— 4 



