PHOSPHORUS FROM CASEINOGEN. 445 



curve for soluble P 2 5 . The presence of soluble P 2 O 5 cannot therefore 

 account for the continued increase of electrical conductivity, though the 

 preliminary rapid rise of electrical conductivity might be partially 

 explained by the presence of phosphates as electrolytes 1 . 



In Experiments 4 and 5 the determinations of soluble P 2 O S were 

 carried on for several days, not only in the tannic acid filtrate, but also 

 in the filtrate obtained after adding an equal volume of 5/ trichloracetic 

 acid. Tannic acid was found to be a better precipitant than trichloracetic 

 acid, which, from the data, did not completely precipitate albumoses 

 which would presumably be present after 30 minutes' digestion. In 

 Experiment 5 tannic acid in neutral solution was tried as precipitant in 

 two samples; under these conditions its power of precipitating was not 

 very different to that in acid solution, so that its use was not continued. 

 The amount of alkali in this experiment was only just sufficient to dissolve 



N 

 the caseinogen (Laqueur and Sackur (12) give 0*8 c.c. -z- alkali for 1 gm. 



caseinogen) ; in the previous experiments it was in such amount as to 

 redden phenolphthalein. 



Experiment 6 was carried out in a solution containing no alkali, so 

 that the acidity was that of the caseinogen itself; as expected, the rate 

 of separation of soluble P 2 5 was much slower. This is partly due to 

 small lumps of caseinogen and partly to the retarding effect of acids 

 upon the action of trypsin. 



It will be observed that, in every experiment, the whole of the 

 phosphorus of caseinogen did not pass into solution, a small quantity 

 being always precipitated by the tannic acid. An indigestible residue 

 containing phosphorus, which was precipitated on acidifying tryptic 

 digests of caseinogen, had been observed by both Sebelien (2) and Biffi (3) , 

 who came to the conclusion that it had no relation to the caseinogen, 

 but was derived from the trypsin, since its amount was greater when 

 the quantity of ferment was increased. 



Upon this point we have carried out a series of experiments, since 

 estimations of the phosphorus in trypsin did not give an amount 

 sufficient to account for it. 



20 c.c. filtered 8/ trypsin solution gave 17'5 mgm. P 2 6 . 



20 c.c. filtered 3 / trypsin solution after precipitating by tannic acid gave 12'6 mgm. 

 P 2 5 . 



i.e. 0'6 gm. trypsin contains 5 mgm. residual phosphorus, and a 50 c.c. sample, when 

 the digest contains 0-3 / ferment, contains 1-2 mgm. 



1 This point will be dealt with in greater detail in a future paper by one of the present 

 authors. 



