1906.] 



The Viscosity of the Blood. 



351 



pressures as etretinates. Over the present range of pressures it will be seen 

 that a small change of pressure at, e.g., 10 cm. Hg, will cause a greater 

 diminution of the outflow time for blood poor in corpuscles than for blood 

 rich in corpuscles and, as a consequence of this, in the human circulatory 

 system we should find such changes producing a much more rapid return of 

 the arterial blood to the heart. Further reference will be made to this 

 point, however, in the subsequent discussion of the bearing of this and 

 foregoing results on the disorders of the circulatory system. Below about 

 5 cm. pressure the curves would seem to indicate that this effect is not so 

 much en evidence. Similar results and curves, though naturally with smaller 

 values for t\, were obtained when these observations were repeated at higher 

 temperatures. 



Summary. 



The chief results of the foregoing investigations may be briefly summarised 

 in the following general statements : — 



1. The decrease in viscosity for each degree rise of temperature is less 



marked for plasma than for blood. 



2. It is also decidedly less for blood containing few corpuscles per cubic 



millimetre than for blood containing many corpuscles per cubic 

 millimetre. 



3. For any given temperature and capillary bore an increase in the number 



of corpuscles causes an increase in the viscosity (cf. Tables I— III), 

 though it is to be remarked that — 

 (a) with tubes of wide bore a very large increase in the number of 

 corpuscles is necessary to cause an appreciable effect (cf. Table VI), 

 whereas 



(&) with small capillaries a slight increase in the number of corpuscles 

 always causes a very marked increase in the viscosity (cf. Table V). 



4. With a given number of corpuscles the rate of flow through any 



particular tube down to about 3 mm. in diameter is, over the range 

 of pressure occurring in living organisms, practically directly 

 proportional to the pressure. 



5. A given increase of pressure exerts a much greater accelerating effect 



on the rate of flow through tubes of fine calibre than through tubes 

 of wider bore. 



6. The influence of a definite increase of pressure on the time of flow is 



slightly less for blood at fever temperatures than for the same blood 

 at lower temperatures. 



7. The pressure influence is also greater for blood containing a large 



2 E 2 



