358 



The Viscosity of the Blood. 



and hence, if we neglect the differences of densities, 



n'/n" = t'/t", 



a result which should in general be correct to about 1 per cent. 



In using these tubes the following points must be observed, otherwise 

 serious discrepancies and much difficulty will be encountered. 



1. The tubes ought to be scrupulously clean and after use are best cleaned 

 as follows : — The blood is at once driven out by a small force pump in order 

 that clotting may not occur in the tube. The viscosimeter is then filled with 

 strong nitric acid and placed aside for a short time, the acid is next replaced 

 in quick succession by distilled water, alcohol and ether, and the tube finally 

 dried by blowing a current of air through it. 



2. The viscosimeter should be previously brought to the temperature of the 

 patient. 



3. It is absolutely necessary to fill the receptacle with blood, for if the 

 column of blood in the capillary breaks from the fact that there is an 

 insufficiency, the experiment is utterly useless on account of the altered 

 pressure height which the method presupposes constant. 



4. It is a wise precaution to fix on to the short limb of the tube a small 

 piece of rubber tubing, so that, if the blood should at first refuse to flow 

 through the instrument, movement may be initiated by slight suction. 



5. Determinations of the viscosity of the blood should be accompanied by 

 a careful blood count and observation of the temperature. 



6. In these estimations a good assistant will be invaluable, whose care it 

 should be to time the rate of flow. 



