92 THE BLOOD. 



to a greater or less degree, affect the blood also, it might 

 be expected that considerable variations in the qualities of 

 this fluid would be found under different circumstances of 

 disease ; and such is found to be the case. Even in health, 

 however, the general composition of the blood varies con- 

 siderably. 



The conditions which appear most to influence the com- 

 position of the blood in health, are these : sex, pregnancy, 

 age, and temperament. The composition of the blood is 

 also, of course, much influenced by diet. 



1 . Sex. The blood of men differs from that of women, 

 chiefly in being of somewhat higher specific gravity, 

 from its containing a relatively larger quantity of red 

 corpuscles. 



2. Pregnancy. The blood of pregnant women has a 

 rather lower specific gravity than the average, from de- 

 ficiency of red corpuscles. -The quantity of white corpuscles, 

 on the other hand, and of fibrin are increased. 



3. Age. From the analysis of Denis it appears that the 

 blood of the foetus is very rich in solid matter, and especially 

 in red corpuscles ; and this condition, gradually diminishing, 

 continues for some weeks after birth. The quantity of solid 

 matter then falls during childhood below the average, again 

 rises during adult life, and in old age falls again. 



4. Temperament. But little more is known concerning 

 the connexion 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 



