THE BLOOD. 



169 



gravity of the blood may be regarded as a safe index of viscosity. 

 The greater the specific gravity the greater the viscosity. Hiirthle 

 has estimated that the work done by the heart in the dog is more 

 than four times as great as it would be if the circulation contained 

 distilled water instead of blood. This difference is due to the 

 viscosity, which is 4.7 times that of water. 



In cholera, the viscosity of the tarry blood is so much it will not 

 run through the capillaries. PolycythaBmia also increases the vis- 

 cosity. Here the capillary circulation is slowed and the extremities 

 are cold or dusky. Alcohol, by the digestive tract or by vein, makes 

 the viscosity greater. 



Fig. 46a. Viscosimeter of Ostwald. 



The tube is filled with a measured quantity of blood. Suction is made in 

 the tube A until the blood rises up to the mark C. Then the blood, by its own 

 pressure, is permitted to fall to the mark D. In a like manner a similar quan- 

 tity of water is used. The time occupied in the fall from C to D of these fluids 

 is compared. (ASHER.) 



Quantity of Blood. From very early times the theme of the 

 quantity of blood circulating within the body has been uppermost 

 in the minds of physiologists and investigators. By reason of the 

 methods then employed the results were inaccurate and difficult 

 of attainment. Simple bleeding was resorted to, but deductions 

 depended upon the rapidity with which the blood was lost. If the 

 animal was bled very rapidly, then considerable blood remained in 

 the vessels. If the blood was extracted very slowly, not only blood, 

 but serum from the lymphatic vessels, spaces, and glands was 

 obtained. These factors very materially altered the calculations. 



The accepted, though not very simple, method, for determina- 

 tion of the quantity is that of Welcker's. It is as follows: The 

 specific gravity of the blood as well as weight of the animal are first 



