84 THE BLOOD. 



4. Temperament. But little more is known concerning 

 the connection of this with the condition of the blood, than 

 that there appears to be a relatively larger quantity of solid 

 matter, and particularly of red corpuscles, in those of a 

 plethoric or sanguineous temperament. 



5. Diet. Such differences in the composition of the 

 blood as are due to the temporary presence of various 

 matters absorbed with the food and drink, as well as the 

 more lasting changes which must result from generous or 

 poor diet respectively, need be here only referred to. 



Effects of Bleeding. The result of bleeding is to diminish 

 the specific gravity of the blood ; and so quickly, that in a 

 single venesection, the portion of blood last drawn has often 

 a less specific gravity than that of the blood that flowed 

 first (J. Davy and Polli). This is, of course, due to ab- 

 sorption of fluid from the tissues of the body. The physio- 

 logical import of this fact, namely, the instant absorption 

 of liquid from the tissues, is the same as that of the intense 

 thirst which is so common after either loss of blood, or the 

 abstraction from it of watery fluid, as in cholera, diabetes, 

 and the like. 



For some little time after bleeding, the want of red 

 blood-cells is well marked; but, with this exception, no 

 considerable alteration seems to be produced in the com- 

 position of the blood for more than a very short time, the 

 loss of the other constituents, including the pale corpuscles, 

 being very quickly repaired. 



Variations in the Composition of the Blood, in different Parts 

 of the Body. 



The composition of the blood, as might be expected, is 

 found to vary in different parts of the body. Thus arterial 

 blood differs from venous ; and although its composition 

 and general characters are uniform throughout the whole 

 course of the systemic arteries, they are not so throughout 



