256 THE BLOOD. 



the fact that in the removal of the proteins a small amount of proteose- 

 like substance is formed from other proteins (namely from the globin 

 of the blood pigment), and on the other hand the proteoses can be pre- 

 cipitated with the other bodies. The question as to the physiological 

 occurrence of proteoses in the blood or plasma must be considered as 

 still undecided. 1 



In close relation to the proteoses stands perhaps the above-men- 

 tioned seromucoid, which was discovered by ZANETTI and especially 

 studied by BYWATERS. It is a glycoprotein which is soluble in water, 

 and precipitated by alcohol. Seromucoid contains according to BY- 

 WATERS 2 11.9 per cent N, 1.8 per cent S, and yields approximately 25 

 per cent glucosamine. The quantity in the blood is 0.20.9 p m. 



The Blood-serum. 



As above stated, the blood-serum is the clear liquid which is pressed 

 out by the contraction of the blood-clot. It differs chiefly from the 

 plasma in the absence of fibrinogen and in containing an abundance 

 of fibrin ferment. Considered qualitatively, the blood-serum contains 

 the same chief constituents as the blood-plasma. 



Blood-serum is a sticky liquid which is more alkaline toward litmus 

 than the plasma. The specific gravity in man is 1.027 to 1.032, average 

 1.028. The color is more or less yellow; in human blood-serum it is 

 pale yellow with a shade toward green, and in horses it is often amber- 

 yellow. The serum is ordinarily clear; after a meal it may be opales- 

 cent, cloudy, or milky white, according to the amount of fat contained 

 in the food. 



Besides the above-mentioned bodies, the following constituents are 

 found in the blood-plasma or blood-serum: 



Fat occurs from 1-7 p. m. in fasting animals. After partaking of 

 food the amount is increased to a great extent. Fatty acids, or soaps, 

 glycerin (NiCLOux, FR. TANGL, and ST. WEISER 3 ) lecithin and cholesterin 

 are also found. Cholesterin occurs, according to HuRTHLE, 4 at least 

 in part, as fatty-acid esters (serolin according to BOUDET). According 

 to LETSCHE 5 free cholesterin probably also occurs in the serum. 



Sugar seems to be a physiological constituent of the plasma and 



1 See especially Abderhalden, Zeitschr. f. physiol. Chem., 51, and Biochem. Zeitschr., 

 8 and 10, and E. Freund, ibid., 7 and 9, which also contains the literature. 



2 Biochem. Zeitschr., 15. 



3 Nicloux, Compt. rend. soc. biol., 55; Tangl and St. Weiser, Pfliiger's Arch., 115 



4 Zeitschr. f. physiol. Chem., 21, where Boudet is also cited. In regard to the 

 quantity of these esters in bird-serum, see Brown, Amer. Journ. of Physiol., 2. 



5 Zeitschr. f . physiol. Chem., 53. 



