324 JR, H. Chittenden — Papoid-digestion. 



The act of curdling, like the process of digestion, is modified 

 more or less by the conditions under which the experiment is tried. 

 Thus, under some circumstances the curdling takes place quickly and 

 the separation of the casein is quite complete. Under others, the 

 curdling takes place slowl}^ and is very incomplete. These points 

 are well illustrated by the following experiments : Each mixture 

 had a total volume of 100 c. c, composed of 25 c. c. of milk, either 

 fresh or boiled as indicated, 25 c. c, of an aqueous solution of papoid 

 (0'5 gram papoid), and 50 c. c. of water containing sodium bicar- 

 bonate as indicated, or else an equal volume of lime water and 

 water as specified. Some of the mixtures were kept at a tempera- 

 ture of 40-45° C, while others were allowed to stand at the room 

 temperature, viz : 22-24° C. Following, are the results obtained 

 under the different conditions : 



I 









At 



40-45° C. 







Character ot the milk. 





Reaction of the mixture. 



Time of curdling. 



Boiled 







Neutral 



3 minutes 



Fresh 









1 1 



10 





( i 



10 per 



cent 



;. lime water 



11 





a 



20 







(( 



12 





li 



2-0 







Bicarb, soda* 



19 





a 



1-0 







< k 



35 





<• 



0-5 







(( 



55 



'• 



Boiled 



2-0 







(( 



240 



(( 



In the presence of 2*0 per cent, sodium bicarbonate, the boiled 

 milk was very incompletely curdled ; apparentl}'-, the digestion of 

 the casein was quite advanced before any sign of separation could 

 be observed. In the neutral solution, on the other hand, the curd- 

 ling of the boiled milk took place almost immediately, as noted, and 

 was at the same time very complete, the casein separating as a fine 

 flocky precipitate, leaving an almost clear fluid. On longer stand- 

 ing at 40° C, the separated casein was, however, gradually dis- 

 solved. In the presence of 0*5 and TO per cent, sodium bicarbonate, 

 the curdling of the fresh milk was not as complete as when 2*0 per 

 cent, of the bicarbonate was present. This would naturally be ex- 

 pected, since the longer the curdling is delayed the less unaltered 

 casein will there be to separate. In all of the above cases where the 

 curdling took place inside of 20 minutes the separation of the casein 

 was fairly complete. 



* The percentages refer to the total amount of bicarbonate, or other substance, con- 

 tained in the 100 c. c, of fluid. 



