76 THE BLOOD. 



of the hepatic vein, but disappearing during its transit through 

 the lungs (Bernard) ; urea, and in very minute quantities, 

 uric add (Gar rod); hippuric and lactic acids; ammonia (Rich- 

 ardson); and, lastly, certain coloring and odoriferous matters. 



Variations in healthy Blood under different Circumstances. 



As the general condition of the body depends so much on 

 the condition of the blood, and as, on the other hand, any- 

 thing that affects the body must sooner or later, and to a 

 greater or less degree, affect the blood also, it might be ex- 

 pected 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 considerably. 



The conditions which appear most to influence the compo- 

 sition 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 deficiency of red 

 corpuscles. The quantity of white corpuscles, on the other 

 hand, and of fibrin, is 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 

 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 ab- 

 sorbed with the food and drink, as well as the more lasting 

 changes which must result from generous or poor diet respect- 

 ively, 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 draw r n has often 

 a less specific gravity than that of the blood that flowed first 



