264 THE BLOOD. 



Proteose-like substances have been found in blood-serum by several 

 investigators, and NOLF l has shown that after the abundant introduc- 

 tion of proteoses into the intestine, they pass into the blood. BOR- 

 CHARDT 2 has also been able to show that not only after the introduction 

 of elastin-proteose per os, but also after feeding dogs with not over- 

 abundant quantities of elastin, a proteose, hemielastin, passes into the 

 blood and can indeed be eliminated in the urine. The question whether 

 the proteoses are normal constituents of the blood under ordinary con- 

 ditions is still much disputed. The difficulty in deciding this ques- 

 tion lies in 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 

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

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

 still undecided. 3 



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, 4 11.6 per cent N, 1.8 per cent S, and yields approximately 25 

 per cent glucosamine. The quantity in the blood is 0.2-0.9 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. Otherwise 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: 



1 Bull. Acad. Roy. Belg., 1903 and 1904. 



2 Zeitschr. f. physiol. Chem., 51 and 57. 



3 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. 



4 Biochem. Zeitschr., 15. 



