BLOOD AND LYMPH 259 



active in acid medium and present in mononuclear cells. It is claimed 

 that the granular leucocytes originate in the bone marrow, whereas 

 the non-granular leucocytes (lymphocytes) have a lymphatic origin 

 (lymph glands or lymphoid tissue) ; this matter of origin is uncertain. 

 The normal number of leucocytes in human blood varies between 5000 

 and 10,000 per cubic millimeter. The ratio between the leucocytes and 

 erythrocytes is about i 1350-500. A leucocytosis is said to exist when 

 the number of leucocytes is increased for any reason. Leucocytoses 

 may be divided into two general classes, the physiological and the 

 pathological. Under the physiological form would be classed those 

 leucocytoses accompanying pregnancy, parturition and digestion, as well 

 as those due to mechanical and thermal influences. The leucocytoses 

 spoken of as pathological are the inflammatory ^infectious, post-hemor- 

 rhagic, toxic and experimental forms, as well as the type of leucocytosis 

 which accompanies malignant disease. 



The blood plates (platelets or plaques) are round or oval colorless 

 discs which possess a diameter about one-third as great as that of the 

 erythrocytes. Upon treatment with certain reagents, e.g., artificial 

 gastric juice, they may be separated into a homogeneous, non-refractive 

 portion and a granular, refractive portion. The blood plates are 

 associated with the coagulation of the blood. This relationship is not 

 completely understood at present. 



The hemoconein or so-called "blood dust" is made up of round 

 granules which usually have a diameter somewhat less than i micron. 

 The serum of normal as well as of pathological blood contains these 

 granules. They were first described by Miiller to whom they appeared 

 as highly refractile granules possessed of Brownian movement. The 

 "blood dust" is apparently not concerned with the coagulation of the 

 blood. The granules are insoluble in alcohol, ether and acetic acid 

 and are not blackened by osmic acid. According to Miiller, the gran- 

 ules making up the so-called "blood dust" constitute a new organized 

 constituent of the blood, whereas other investigators believe them to be 

 merely free granules from certain of the forms of leucocytes. They 

 appear to possess no clinical significance. 



The processes involved in the coagulation of the blood are not fully 

 understood. Several theories have been advanced and each has its 

 adherents. The theory which appears to be fully as firmly founded 

 upon experimental evidence as any is the following: Blood contains a 

 zymogen called prothrombin which combines with the calcium salts 

 present to form an enzyme known as thrombin or fibrin-ferment. When 

 blood is drawn from a vessel the fibrin-ferment at once acts 

 upon the fibrinogen present and gives rise to the formation of fibrin. 



