THE BLOOD. 153 



contains more than venous, blood. There is but little in the portal 

 vein, less in the splenjc, and a mere trace or none at all in the he- 

 patic. We shall recur (p. 158) to its uses in the blood, and its rela- 

 tions to the tissues, after speaking of the other elements in the 

 plasma. 



The serum is best obtained, in its isolated state, from coagulated 

 blood, after the contraction of the clot has ceased. It is sometimes 

 seen to contain a quantity of undissolved particles in suspension, 

 which give it a milky appearance, and which consist of fat-globules, 

 granules of precipitated albumen, or of colorless (cytoid) blood- 

 corpuscles. 



The amount of water in the serum is generally directly propor- 

 tioned to that in the whole blood, and inversely to the number of 

 the blood-corpuscles. A very watery serum, however, necessitates 

 an increase of water in the individual blood-corpuscles, from endos- 

 mosis. In the serum of the blood of adult males it averages 90.5 

 per cent.; in that of females, especially during pregnancy, somewhat 

 more. Arterial blood contains more water than that of the veins ; 

 that of the portal vein, however, contains the most water of all of 

 the latter, especially during digestion, and the blood of the hepatic 

 vein less than that of any other vessel. The serum becomes more 

 watery in most diseases, except in the first stages of typhus fever, 

 measles, scarlet fever, and cholera. The blood of the amphibia 

 contains more water, and that of birds less, than the blood of the 

 mammalia. 



The principal constituent of the blood-serum is albumen, of which 

 there is from 7.9 to 9.8 per cent.; and from 63 to 70 parts 1 in 1,000 

 of blood. (Becquerel and Rodier^) Arterial blood contains less albu- 

 men than venous; in the horse, as 9.2 to 11.4. (Lehmann.) The 

 blood of the hepatic vein is very rich in it, while the portal vein 

 has still less than the arteries. The quantity of albumen in the 

 blood of the veins increases considerably during digestion. Human 

 blood contains, on an average, more albumen than that of most 

 mammalia. In most diseases the amount of albumen is diminished, 

 it having been found increased only in plethora, intermittent fever, 

 and cholera. < * - 



It is not yet satisfactorily demonstrated that caseine exists in the 



1 This includes about 4 parts of albuminose. (Robin and Verdeil.} Lehmann's 

 analysis would, however, give only about 44 in 1,000 parts of blood, which is pro- 

 bably nearer the fact. 



