v THE BLOOD : PLASMA 129 



first, the total weight of the proteins coagulated by alcohol or by heat. The 

 percentage amount of serum albumin can be calculated from the difference 

 t>etweeii the two values. 



Estimation of Sero-mucoid. I. To prepare and simultaneously estimate 

 sero-mucoid, Zanetti used the same method Morner employed for ovo-mucoid. 

 The proteins are first precipitated from a given amount of blood serum 

 diluted witli two volumes of 10 per cent NaCl solution, by coagulation, after 

 previous acidification with acetic acid. The filtrate is evaporated on the 

 water bath to a reduced volume, and is then treated with alcohol. To 

 purify the precipitate obtained, which consists of sero-mucoid, it is again 

 dissolved in water, and reprecipitated with alcohol. This operation is 

 repeated five or six times, till a very slightly coloured precipitate is obtained,, 

 which can be collected on a filter that has been previously dried and 

 weighed. After repeated washing with ether, the substance is dried in vacuo 

 over sulphuric acid till the weight is constant. The sero-mucoid appears as 

 a light straw-coloured powder. It is somewhat hygroscopic, dissolves in 

 warm water, and gives all the reactions of mucoid substances. Its property 

 of reducing Fehling's solution after previous boiling with hydrochloric acid,, 

 led Zanetti to term it gluco-protein. 



III. The various proteins differ little in their percentage com- 

 position, and are probably derived from the molecular complex 

 into which the different nuclei or groups of atoms have entered 

 in different relations. In fact, when broken up by steam at high 

 pressure, or by prolonged boiling with dilute alkali or mineral 

 acids, they invariably yield the same products, viz. ammonia, 

 hydrogen sulphide, and a series of ammo-acids, among which 

 tyrosine, leucine, and asparaginic acid are always present. Since 

 tyrosine is a compound of the aromatic series, and leucine and 

 asparaginic acid are two bodies of the fatty series, we may conclude 

 that atomic groups of both series enter into the protein molecule. 



Within the body, however, in consequence of the metabolic 

 activity of the living elements of the tissues, the proteins give 

 rise to a large number of decomposition products, which are 

 either simple waste products, destined as such to be eliminated 

 by the various excretory organs, or products of internal secretion, 

 destined to fulfil other functions and to undergo further trans- 

 formations before they are eliminated. For the most part these- 

 consist of the constituents of urine, which are excreted by the 

 kidneys, among the most important being creatine, creatinine, uric 

 acid, hippuric acid, carbamic acid, and urea. All these are nitro- 

 genous compounds, and are therefore derived from retrogressive 

 or katabolic metamorphoses of the proteins. 



As these waste products are promptly eliminated as fast as 

 they reach the blood plasma, they can obviously exist there only 

 in very minute quantities. As a matter of fact, urea and 

 ammonia are the sole constituents of urine that can be isolated 

 from blood serum, urea only in an amount of which the maximum 

 does not exceed O05 per cent (I. Munk), ammonia in an average 

 amount of O79 mgrni. to each 100 grins, of blood (Beccari). Creatine 

 and uric acid are found in much smaller quantities; hippuric 



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