1906.] 



The Viscosity of the Blood. 



353 



metabolic products contained in the circulating blood, which alterations in 

 themselves tend to raise the viscosity. 



Apart, therefore, from the raised temperature, these changes in the 

 mechanism would tend to throw more work upon the heart, which, however, 

 owing to its great reserve force, can respond for a time ; fortunately in most 

 cases, before it begins to flag, the second stage, or fastigiuni, is reached, in 

 which the peripheral resistance is relaxed. This loss of vasomotor tone is 

 always a noticeable feature at this period, and as a result the work of the 

 heart is once more considerably lightened. Experimental evidence has given 

 abundant proof of the marked increase in the rate of flow that follows upon 

 a widening of the conducting channel ; and further, our results have shown 

 that with fine capillaries this influence is considerably greater than the 

 fourth power of the radius, as is stated in Poiseuille's formula. 



We would emphasise here again the marked influence of temperature on 

 the viscosity of all fluids ; for instance, the viscosity of water at 30° C. is one- 

 half of what it is at 0° C, whilst with blood containing some 5 - 10 6 red 

 corpuscles per cubic millimetre, our Tables, in some cases, show as large a 

 change as 3 per cent, per 1° C. 



Now the usual reasons given for the more rapid beating of the heart are : 

 (1) the disturbance of the nerve centres ; (2) the direct action of the patient's 

 overheated blood upon the heart muscle. This last statement is founded 

 upon the experimental ground that by perfusing an isolated mammalian 

 heart with warm blood there results a more frequent contraction. Now we 

 would add a third reason : the more rapid filling of the heart as a result of 

 (1) the lessened resistance; (2) the diminished viscosity; therefore, as a con- 

 sequence of the increased rate of flow, the diastolic period of the heart is 

 lessened, and the ventricles refill much more quickly. 



To quote Dr. Graham Brown, " a febrile temperature may be considered 

 as a boon to the organism, in that it will allow the blood to circulate faster 

 or it will save the work of the heart " ; a deduction of the utmost 

 importance, and one which, so far, has apparently received very little 

 notice. 



Effect of Change in Calibre of Vessels. 



Again, alterations in the capacity and in the actual structure of the vessels 

 are far from uncommon as the results of disease. The lesion which may 

 follow an infection or intoxication is, unfortunately, not limited, but usually 

 involves, step by step, the whole arterial tree. We may take as an instance 

 of this condition the arterio-sclerosis which occurs in chronic nephritis ; in 

 these cases it is the smaller vessels that are attacked first and their lumen 



