TRYPTIC DIGESTION 35 



Experiments 16 to 19 show the effect of using increasing amounts of- 

 hydrochloric acid with the same trypsin preparation, and experiments 20 

 and 21 show this again with another sample of trypsin. 



Similar results have been obtained with many aqueous extracts of pancreas 

 prepared in the laboratory, and it may be stated generally that the higher 

 the proportion of nitrogen contained in such an extract the larger the amount 

 of hydrochloric acid which must be added in order to prevent destruction of 

 the trypsin by heat. 



In a few cases, as for example experiments 18 and 19, it was found that 

 the protection against heat afforded by a certain amount of acid was the same 

 as regards digestion both of fibrin and of caseinogen. Usually, however, the 

 destruction of the fibrin digesting power was considerably greater than that 

 of the caseinogen digesting power. 



It has been pointed out by Mellanby and Woolley [1913] that in acid of 

 the strength of 0-05 N (HCl) trypsin is slowly destroyed at 16° and more 

 rapidly at 35°. Apparently at room temperature about half the trypsin is 

 destroyed in four hours, and two-thirds is destroyed in a day. The activity 

 of the trypsin in their experiments was measured by its power of coagulating 

 calcified milk. Other references to the effect of hydrochloric acid on trypsin 

 at moderate temperatures have been mentioned in a previous paper [Edie, 

 1914]. It was also found by Lenard [1914] that if trypsin is rendered inactive 

 by addition of acid, only a trace of its activity is restored by neutralising and 

 then adding alkali. These observers appear only to have tested the activity 

 of the trypsin on one substrate, but in the following experiments the action 

 of hydrochloric acid on trypsin at room or body temperature has been tested 

 as regards the power to digest both fibrin and caseinogen. In these experi- 

 ments alcohohc (15 %) extracts of pig's pancreas were used. These were 

 practically neutral. In every case 1 cc. of the original trypsin was compared 

 with that quantity of the trypsin + acid which would contain 1 cc. of trypsin 

 originally, and the solutions so adjusted as to contain the same amount of 

 sodium chloride. Digestion both of fibrin and of caseinogen was carried on in 

 presence of 0-5 % sodium carbonate, 1 g. fibrin or 0-6 g. caseinogen being 

 used, in about 40 cc. of fluid. The amount of digestion is expressed, as usual, 

 in cc. of iV/10 nitrogen. 



22. 10 cc. trypsin + 20 cc. N HCl. Kept at 36° for 12 min. 20 cc. N NaOH then added. 



Digestion by control 21-6 cc. fibrin, 38'2 cc. caseinogen. 



„ treated trypsin 0-0 cc. „ 8-8 cc. „ 



23. 20 cc. trypsin + 10 cc. N HCl. Room temperature for 4 days. 10 cc. N NaOH added. 



Digestion by control 12-1 cc. fibrin, 31-6 cc. caseinogen. 



„ treated trypsin 0-0 cc. ,, 5-4 cc. „ 



24. 40 cc. trypsin + 20 cc. N HCl. Room temperature for 11 days. 20 cc. N NaOH added. 



Digestion by control 11-7 cc. fibrin, 38-7 cc. caseinogen. 



„ treated trypsin 0-0 cc. „ 5-6 cc. „ 



It will be seen from these experiments that the power of trypsin to digest 

 fibrin is destroyed considerably more readily in acid solution at moderate 



(501) 



