1881.] and Proteolytic Activity of Pancreatic Extracts. 155 



Estimation of the Proteolytic Activity of Pancreatic Extracts — Trypsimetry. 



The writer had found in previous inquiries that when milk is sub- 

 jected to digestion with pancreatic extract, a striking change takes 

 place in it at an early stage of the process. The milk acquires the pro- 

 perty of curdling when boiled. The onset of this reaction occurs at an 

 earlier or at a later period according to the activity of the extract and 

 the quantity of it employed ; and it is possible to fix the time of its 

 advent with considerable accuracy — sufficient accuracy to serve as the 

 basis of a method of measuring the proteolytic activity of pancreatic 

 extracts. 



The reaction in question depends on the production, as a first step in 

 the pancreatic digestion of casein, of a modified form of that body 

 which I have named metacasein. This substance resembles casein in 

 being curdled by acetic acid in the cold ; but it differs from casein in 

 being also curdled by simple boiling. These two reactions together 

 distinguish metacasein from other proteid bodies. 



The property of curdling when boiled, which may be called the 

 metacasein reaction, continues observable in milk undergoing tryptic 

 digestion until near the termination of the process ; it then disappears 

 somewhat abruptly, and the milk, when boiled, remains fluid just as it 

 did at first. 



We may, therefore, speak of the onset point of the metacasein reaction, 

 .and of the vanishing point of the metacasein reaction. These two 

 points mark respectively the initial and the terminal limits of the 

 principal phase in the digestion of milk by pancreatic extract. 



Before the onset point of the reaction — that is, distinct and un- 

 doubted curdling — is actually reached, its approach is indicated by an 

 appearance of soiling of the sides of the test-tube in which the milk 

 has been boiled. This appearance is due to incipient coagulation, 

 which presently developes into pronounced curdling, and is a useful 

 sign in testing to indicate the coming on of the metacasein reaction. 



The following typical experiment may serve to give the reader a 

 clear notion of the succession of events — so far as they concern us 

 here — which occur when milk is submitted to digestion with pan- 

 oreatic extract. 



Table V. 



4 cub. centims. pancreatic extract added to 50 cub. centims. milk 

 diluted with water to 100 cub. centims. Temp. 18° C. 



Time. Reaction on boiling. 



2 minutes . . No change. 



3 „ . . Slight soiling of the sides of the test-tube. 



4 „ . . More soiling. 



5 „ . . Distinct curdling — onset point of the meta- 



casein reaction. 



