CHAP. II.] THE BLOOD. 65 



Neutral When serum is evaporated to dryness and the 



ies 11111 res ^ ue ^ s powdered and boiled with ether, this liquid 

 terin extracts all the above bodies. Especially is this the 



case when the serum presents, as it does some hours 

 after food, the milky appearance which has already been described. 

 The serum of fasting animals contains on an average about 0'2 per 

 cent, of fats and cholesterin, that of animals in digestion may 

 contain from 04 to 0'6 p.c. The fats present in the serum are 

 triolein, tristearin, and tripalmitin. It was formerly believed that in 

 addition to these fats, soaps, i.e. alkaline salts of the fatty acids, were 

 present in the blood. The incorrectness of this surmise has been 

 demonstrated by Rohrig 1 , who has shewn that soluble soaps cannot 

 exist in the blood. 



Cholesterin, which will be studied in connection with the 

 chemistry of the nervous organs, may constitute 10 p.c. of the ether 

 extract of blood. It has been found by Hoppe-Seyler 2 to vary in 

 the serum of the blood of fattened geese from 0*019 to 0'314 per cent. 

 Besides the fats and cholesterin the serum of blood always. contains, 

 according to Hoppe-Seyler, some lecithin; this ^substance will be 

 treated of under ' brain.' 



Sugar. Glucose is a normal constituent of the blood, and is 



contained in the serum which separates from it after coagulation. Its 

 amount appears, according to the most recent researches. (Abeles 3 , 

 Pavy 4 , v. Mehring 5 ), to be nearly the same in the blood of all the 

 vessels with the one exception of the blood of the portal vein, which 

 contains an excess of sugar after the ingestion of a saccharine diet. 



The quantity of glucose present in the blood of the dog was found 

 by Pavy to vary between 0*81 and 1*231 parts per 1000. 



In the experiments of v. Mehring, the amount of sugar in the 

 serum of dogs was found to vary between 0'125 and 0'330 p.c. This 

 matter will be fully treated of under 'liver' and 'nutrition' (see also 

 Chapter IV.). 



Creatine, creatinine, urea, carbamic acid, xanthine, 

 acid^Crea- ' hypoxanthine, uric acid and hippuric acid are found in 

 tine,' &c. the serum. The amount of urea present in the normal 



blood of man varies between 02 and 0'04 p.c. 



A yellow pigment is found dissolved in the serum of the blood of 

 man and most animals, although certairj. animals (e. g. the rabbit) 

 have colourless serum. 



1 Rohrig, "Ueber die Zusammensetzung und das Schicksal der in das Blut eingetre- 

 tenen Nahrfette." Ludwig's Arbeiten, 1874. 



2 Hoppe-Seyler, "Ueber das Vorkommen von Cholesterin und Protagon und ihre 

 Betheiligung bei der Bildung des Stroma der rothen Biutkorperchen." Med. Chem. 

 Untersuchungen, p. 145. 



3 Abeles, " Der physiologische Zuckergehalt des Blutes." Med. Jahrbucher, Heft 

 in., 1875 ; also MaJj's Jahresbericht, Vol. vi. p. 95. 



4 Pavy, " The Croonian Lectures on certain points connected with Diabetes.' 

 London, 1878. 



5 v. Mehring, " Ueber die Abzugswege des Zuckers aus der Darmhohle." Archiv f. 

 Anat. u. Physiol. 1877, pp. 380415. 



a. 5 



