R. M. Chittenden — Papoid-digestion. 325 





At 33-24° C. 





Character of the milk. 



Reaction of the mixture. 



Time of curdling. 



Boiled 



Neutral 



12 minutes. 



Fresh 



(( 



145 " 



Boiled 

 Fresh 



20 per cent, lime water \ 



2-0 " Bicarb, soda i" 



J 



Not curdled at 



the end of 4 



hours. 



It is thus evident, from the above experiments, that the curdling 

 of milk by papoid is greatly modified by the temperature of the 

 fluid. It is not to be assumed, however, that while precipitation of 

 the casein is delayed b}^ a low temperature, digestion is equally 

 retarded. Such is certainly not the case, for digestion of the casein, 

 whether still in solution or precipitated by the curdling process, 

 unquestionably goes on, although naturally at a slower rate than at 

 a higher temperature. In other words, the rate at Avhich curdling 

 is produced is not necessarily to be taken as a measure of the prob- 

 able rate of proteolytic action on the proteids of the milk. The 

 two processes are, without doubt, wholly independent, and in the 

 case of predigesting milk, where naturally a smaller proportion of 

 papoid is used than in the above experiments, the necessary diges- 

 tion is accomplished without any accompanying separation of the 

 casein ; whether it be carried on at a low temperature, or at a tem- 

 perature of 45° C. ; and in the presence of water alone, or in the 

 presence of sodium bicarbonate, or lime water. 



Hence, in order to curdle milk, fresh or boiled, a fairly large pro- 

 portion of papoid must be employed, while for the partial digestion 

 of milk a far smaller proportion will accomplish the desired result, 

 and that without necessarily causing any preliminary separation of 

 the casein. From this we may infer either that the proteolj^tic fer- 

 ment is present in larger quantity in papoid than the rennet-like 

 ferment, or else that it is far more active than its neighbor, the 

 milk-curdling: ferment. 



In predigesting milk with papoid, or any other ferment, the main 

 object sought is the partial digestion of the casein ; this being, as is 

 well-known, the most imj^ortant proteid of milk, and at the same 

 time the one most liable to cause trouble in the feeding of infants, 

 and others, with weak digestion. In order to test the digestive 

 action of papoid on this proteid, the casein was separated from 

 fresh milk by precipitation with dilute acid, partial!}^ purified by 

 re-solution in alkaline water, and reprecipitation witli acid. It was 

 then washed with water, and though still containing some adherent 



