BLOOD. 347 



has much positive evidence in its favor. It remains possible, on the one 

 hand, that all these as well as other functions may be performed by the 

 leucocytes, and, on the other hand, further discoveries may give an entirely 

 new explanation of the value of these cells to the body. As to the origin of 

 the leucocytes, it is known that they increase in number while in the circu- 

 lation, 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 l recently demonstrated 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 multinucleated leucocytes go to pieces in the blood the 

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

 blood-plates, which 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 which is eliminated 

 from the body. The specific function, if any, of the blood-plates, beyond 

 that of 'aiding in coagulation, remains to be discovered. 



B. CHEMICAL COMPOSITION OP THE BLOOD ; COAGULATION ; TOTAL 

 QUANTITY OP BLOOD ; REGENERATION AFTER HEMORRHAGE. 



Composition of the Plasma and Corpuscles. Blood (plasma and cor- 

 puscles) contains a great variety of substances, as may be inferred from its 

 double relations to the tissues as a source of food-supply and as a means of 

 1 Du Bois-Reymond's Archiv fur Physiologic, 1893, p. 560. 



