68 



THE SALTS OF THE PLASMA AND SERUM. [BOOK I. 



and phosphoric acid may by suitable methods be directly precipitated 

 from, and correctly estimated in, the serum. They find that whilst 

 the amount of calcium and magnesium estimated by direct precipita- 

 tion agrees exactly with that determined by analysis of the ash of the 

 same quantity of serum, the phosphoric acid does not so agree; in 

 other words the amount of phosphoric acid found in the ash of serum 

 is much larger than that directly precipitated from it. Furthermore 

 Pribram, and after him Gerlach, found that after precipitating directly 

 all the phosphoric acid in the serum, and precipitating all proteids 

 by absolute alcohol, on igniting the filtrate its ash contained phosphoric 

 acid ; the amount thus found added to that directly precipitated 

 agreed very closely with the total quantity of phosphoric acid deter- 

 mined in the ash of serum. Thus in one experiment, 



100 c.c. of serum yielded on direct ignition 0*056 p,c. P S 6 

 by direct precipitation 00108 



in the alcohol extract 0'0325 



by ignition of the ex- 



tracted residue O'OOGO 



0-0493 p.c. 



From this experiment, which may be taken as a type of many 

 others, it results that serum contains a much smaller quantity of 

 phosphoric acid than is present in its ash and that the greater part of 

 the phosphoric acid in the latter is derived from an organic compound 

 soluble in alcohol. The latter result had to a considerable extent 

 been anticipated by Sertoli 1 . 



The phosphoric acid obtained on direct precipitation of the serum 

 doubtless exists as an inorganic compound, but we cannot assert its precise 

 condition ; probably it does not exist as calcium phosphate. At any rate 

 the whole of the phosphoric acid existing in the serum is not sufficient to 

 combine with the calcium of that fluid to form the compound Ca 3 2(PO 4 ), 

 as will be learnt by a study of the following results obtained by Pribram. 



RESULTS OF SEVEN DETERMINATIONS OF THE PHOSPHORIC ACID 

 (CALCULATED 'AS P 2 6 ) AND LIME (CaO) IN 100 c.c. OF SERUM. 



1 Sertoli, " Ueber die Bindung der Kohlensaure im Blute und ihre Ausscheidung in 

 der Lunge." Medicinisch-Chemische Untersuchungen von Hoppe-Seyler. Heft in. (1868) 

 p. 350 et seq. 



