THE BLOOD 261 



tion of the blood. Whenever they are diminished in number, as in purpura 

 and hemophilia, coagulation takes place very slowly. 



THE TOTAL QUANTITY OF THE BLOOD; ITS GENERAL 

 COMPOSITION 



The determination of the total quantity of the blood in an animal is best 

 made by the chromometric method, somewhat modified at present, of 

 Welcker. This consists, first, in bleeding an animal, collecting all the blood 

 it yields, and weighing it; second, in washing out the vessels with a normal 

 saline solution until the fluid comes from the veins clear and free from blood; 

 third, in mincing the tissues of the body, after removal of the contents of the 

 alimentary canal, soaking them in water for twenty-four hours, and then 

 expressing them. All the washings are collected and weighed. A given 

 volume of the normal defibrinated blood, treated with carbon monoxid so as 

 to give it uniform color, is then diluted with water until its tint is identical 

 with that of the washings similarly treated with carbon monoxid. From the 

 quantity of water necessary to dilute the blood the quantity of blood in the 

 washings is readily determined. The animal having been previously 

 weighed and the weight of the contents of the alimentary canal deducted, the 

 ratio of the total weight of the blood to the weight of the body at once be- 

 comes apparent. By this method it has been shown that the ratio of blood 

 to body- weight in a human adult is i : 13; in an infant, i : 19; in a dog, i : 13; 

 in a cat, i 121. 



The more recent investigations of Haldane and Smith and of Plesch 

 with the employment of a different method make it probable that the ratio 

 is approximately i :ig. Thus a man weighing 70 kilos would have 3684 

 grams of blood. 



The amount of blood in the different organs has been determined by 

 ligating the blood-vessels in the living animal, removing the organ, and after 

 allowing the blood to escape subjecting the tissues to the chromometric 

 methods described above. According to Ranke, the volume of the blood is 

 distributed as follows: Heart, lungs, arteries, and veins, J; liver, J; muscles, J; 

 other organs, J. 



General Composition. The results of the analyses of the blood will 

 vary with the animal and the methods employed. The following table, 

 taken from Gad, shows the average composition, expressed in whole numbers, 

 of horse's blood. In essential respects the ratio of the constituents in human 

 blood would not be materially different. 



One thousand parts of blood contain: 



(Water 200 200 



f Hemoglobin 1 16 



Solids 128 -I Other organic matter 10 



( Salts 2 



f Water 604 604 



Fibrin 7 



Plasma 672 



L Solids... 68 



Albumin 52 



Fat i 



Other organic matter 3 



Potassium and sodium salts 4 



Calcium and magnesium salts i 



CHEMISTRY OF COAGULATION 



The changes which eventuate in the formation of fibrin, and hence all 

 the subsequent phenomena of coagulation, are chemic in character; but as 



