ACTIVITY DURING DIGESTION. 25 



in the affirmative, viz., that the properties of the juice do alter during 

 the period of secretion. But the observation, it appears to me, has not 

 been appreciated to its full extent, otherwise it would have become an 

 inexhaustible source of persevering inquiry as to why and how these 

 variations come to pass. Later I shall adduce instances from our store- 

 house of observations dealing with these highly interesting qualita- 

 tive variations of the juice during the separate periods of digestion. 

 Naturally, it will be found that the greatest interest is attached to 

 variations in the ferment content, although, strictly speaking, the re- 

 maining properties of the digestive juices demand an equally careful 

 investigation to arrive at a satisfactory explanation. 



The available material, especially as regards gastric juice, could not 

 be considered sufficient. Experiments with the ordinary gastric fistula 

 permit of only very hypothetical deductions, since they deal, not with 

 pure juice, but with a mixture of juice and food. Nor can Heiden- 

 hain's observations on the isolated fundus be taken as an index 

 of normal digestive work, since the activity of the isolated stomach, 

 after division of its secretory nerves, obviously difters greatly from 

 the normal. The investigations of Heidenhain on the pancreatic 

 secretion in dogs operated upon by his method, must however be recog- 

 nised as scientifically exact, though, unfortunately, the food was not 

 of definite composition. Nor were all the details published ; they 

 merely appeared in Hermann's Encyclopaedic Handbook in condensed 

 form. 



But before I take up the question of our own results, I must 

 draw your attention for a short period to the methods we employed 

 in our study of the digestive juices. The proteolytic power of the 

 iluid was determined by the process of Mett a procedure worked out in 

 this laboratory and since then constantly retained in use. It consists 

 in this ; fluid egg-white is sucked up into a fine glass tube of 1 to 2 

 mm. lumen, and coagulated therein at a definite temperature (!>5 C.). 

 The tube is then cut into small pieces, which are placed in one or two 

 cubic centimetres of the fluid to be investigated. The whole is kept in 

 the thermostat at 37 C. to 38 C., and requires no further watching. 

 Solution of the proteid occurs at the ends of the small glass tubes. 

 After the termination of a certain period, the length of the pieces of 

 tube, and that of the undigested remains of the proteid columns, are 

 measured oft' with the aid of a millimetre scale and a microscope of low 

 magnifying power. The difference gives the length of the digested 

 proteid cylinders in millimetres and fractions of a millimetre. This 

 method leaves nothing to be desired so far as convenience of applica- 

 tion, and clearness with exactness of results is concerned. Test experi- 

 ments specially carried out (Dr. Ssamojloft) have convinced us that the 



