BLOOD. 191 



mental forms as well as the type of leucocytosis which accompanies 

 malignant disease. 



The blood plates (platelets or plaques) are round or oval, color- 

 less 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 probably associated in some way with the coagula- 

 tion of the blood. This relationship is not well understood at 

 present. 



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

 granules which usually have a diameter somewhat less than one 

 micron. The serum of normal as well as of pathological blood 

 contains these granules. They were first described by Muller to 

 whom they appeared as highly refractile granules possessed of 

 Brownian movement. The " blood dust " is apparently not con- 

 cerned with the coagulation of the blood. The granules are insol- 

 uble in alcohol, ether and acetic acid and are not blackened by osmic 

 acid. According to Muller the granules 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. In common with blood 

 plates the " blood dust" possesses 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 freshly drawn blood comes in contact with 

 the air the fibrin- ferment at once acts upon the fibrinogen present 

 and gives rise to the formation of fibrin. This fibrin forms in 

 shreds throughout the blood mass and, holding the form elements 

 of the blood within its meshes, serves to produce the typical blood 

 clot. The fibrin shreds gradually contract, the whole clot assumes 

 a jelly-like appearance and the yellowish serum exudes. If, im- 

 mediately upon the withdrawal of blood from the body, the fluid 

 be rapidly stirred or thoroughly " whipped " with a bundle of 

 coarse strings, twigs or a specially constructed beater, the fibrin 

 shreds will not form in a network throughout the blood mass but 

 instead will cling to the device used in beating. In this way the 



