THE SERUM. 211 



crystallises into beautiful laminae, and which undoubtedly belongs 

 to the group of the true volatile fatty acids. 



With regard to the extractive matters of the serum, it is better 

 to pass them over in perfect silence, than to collect the fragmentary 

 and inconclusive facts regarding them at present in our possession, 

 (see vol. i. page 320.) From the physiology of the metamorphoses 

 going on in the blood, we should be led to suppose that the 

 extractive matters are far more abundant in the intercellular fluid 

 than in the blood-cells, and this view is confirmed by direct expe- 

 riment; for, as is obvious from what has been already stated 

 regarding the composition of the blood, these substances occur more 

 abundantly, both relatively and absolutely, in the serum than in the 

 cells. 



A number of substances were formerly included and concealed 

 among these extractive matters of the blood, and especially of the 

 serum, which have either lately been discovered or which we have not 

 yet succeeded in finding. First amongst these we must place sugar. 

 This has very recently been proved by C. Schmidt* to be an 

 integral constituent of the normal blood of cattle, dogs, cats, and 

 diseased and healthy men. It has been already mentioned, that 

 in consequence of Bernard's discovery of sugar in the liver, I sought 

 for this substance in the blood of the portal and hepatic veins, and 

 found 10 or 12 times as much in the latter as in the former, in 

 which the quantity was very small. 



The method of determining the amount of sugar in the blood 

 is very simple : freshly drawn and defibrinated blood is gradually- 

 treated with 8 or 10 times its volume of alcohol, the mixture being 

 thoroughly shaken ; the coagulum is washed with hot alcohol, and 

 the alcohol of the filtered fluid driven off; the residue is further con- 

 centrated, and then extracted with stronger alcohol, whereby the 

 greater portion of the salts is separated ; a part of the alcoholic fluid 

 is now treated with an alcoholic solution of potash, by which the 

 potash-and-sugar compound and a little extractive matter are pre- 

 cipitated; the precipitated flakes become caked together on the 

 filter, from the action of the air ; we then dissolve them in water, 

 and can determine the sugar qualitatively by Trommer's, and quan- 

 titatively by Fehling's test. Another part of the alcoholic solution 

 (from which the greater part of the salts has been removed in the 

 above-described manner) may be evaporated, dissolved in water, and 

 treated with a little yeast ; and the quantity of sugar can then be cal- 

 culated from the carbonic acid which is evolved. (See vol. i., p. 288.) 

 * Characteristik der Cholera, u. s. w. S. 161 164. 



p2 



