210 PHYSIOLOGY CHAP. 



dissolving in alcohol no longer reddens litmus. On mixing this 

 purified fat with fresh, alkaline, pancreatic juice, and keeping the 

 mixture in the warm chamber at 37 C. with the addition of 

 a little litmus solution, the alkalinity gradually diminishes, 

 till the mixture finally gives an acid reaction owing to the 

 hydrolytic cleavage of the neutral fat, as first perceived by Oh. 

 Bernard and Berthelot. We shall presently see the great 

 importance of the lipolytic action of the pancreatic juice for the 

 utilisation of the ingested neutral fats. 



On adding succus entericus to pancreatic juice the lipolytic 

 activity of the latter is a little increased. It is much reinforced 

 by the presence of bile, even in a small amount. According to 

 Bruno the lipolytic activity of pancreatic juice can be increased 

 20 times with bile. But if the experiment in vitro be pro- 

 longed beyond a certain time, the difference in activity between 

 the pancreatic juice alone, or with bile, diminishes. From the 

 teleological point of view it is an important fact that on adding 

 bile the pancreatic secretion retains its lipolytic activity much 

 longer. 



The lipolytic activity of pancreatic juice is aided by a slightly 

 alkaline medium, but takes place in an acid medium also. 



In order to measure the lipolytic action of pancreatic juice, a certain 

 quantity of the juice and of pure oil is placed in the thermostat at 37 C., 

 and the quantity of ^Vn solution of alkali required to neutralise the fatty 

 acid formed is estimated. 



The proteolytic action of pancreatic juice (due to trypsin) is 

 certainly its most important property. It acts on all proteins 

 with greater or less rapidity. 



Eaw fibrin is more readily dissolved than other proteins, at 

 37-40 C., in 30 min. to 3 hrs. for large quantities, with a small 

 amount of trypsin, and without any symptom of putrefaction. 

 With other proteins that are more slowly digested (coagulated 

 albumin, cheese, meat, etc.), a little salicylic acid, or thymol, 

 chloroform, or ether (Ktihne) may be added to the extract to 

 exclude any trace of putrefaction, or, still better, a small quantity 

 of iodoform, which according to Vandevelde (1907) does no"t 

 interfere with the action of the enzyme. 



Trypsin, unlike pepsin, digestion takes place both in an 

 alkaline and in a neutral or slightly acid medium. The optimum 

 of digestion occurs with an extract made alkaline with 0*3 per 

 cent solution of sodium carbonate. The addition of free mineral 

 acids, even in small quantities, entirely inhibits digestion. The 

 acids combined with metaproteins (at least in small quantities) 

 neither hinder, nor sensibly delay, digestion (Chittenden and 

 Cummins). 



A further difference in the action of gastric and pancreatic 



