240 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



which may be called the optimum temperature, at which the trypsin acts most 

 powerfully ; if, however, the temperature is raised to as much as 70 to 80 C., 

 the enzyme is destroyed entirely. Trypsin has never been isolated in a condi- 

 tion sufficiently pure for analysis, so that its chemical composition is unknown. 

 Extracts containing trypsin can be made from the gland very easily and by 

 a variety of methods. The usual laboratory method is to mince the gland and 

 to cover it with glycerin for some time. In using this and other methods for 

 preparing trypsin extracts it is best not to take the perfectly fresh gland, but 

 to keep it for a number of hours before using. The reason for this is that the 

 enzyme exists in the fresh gland in a preparatory stage, a zymogen (see sec- 

 tion on Secretion), which in this case is called " trypsinogen." Upon standing, 

 the latter is slowly converted to trypsin a process which may be hastened by 

 the action of dilute acids and by other means. An artificial pancreatic juice 

 is prepared usually by adding a small quantity of the pancreatic extract to an 

 alkaline liquid ; the liquid usually employed is a solution of sodium carbonate 

 of from 0.2 to 0.5 per cent. To prevent putrefactive changes, which come on 

 with such readiness in pancreatic digestions, a few drops of an alcoholic solution 

 of thymol may be added. A mixture of this kind, if kept at the proper 

 temperature, digests proteids very rapidly, and most of our knowledge of 

 the action of trypsin has been obtained from a study of the products of such 

 digestions. 



Products of Tryptic Digestion. Tryptic digestion resembles peptic diges- 

 tion in that proteoses and peptones are the chief products formed, but the two 

 processes differ in a number of details. The naked-eye appearances, in the first 

 place, are different in cases in which the proteid acted upon is in a solid form ; 

 for while in the pepsin-hydrochloric digestion the proteid swells up and grad- 

 ually dissolves, under the action of trypsin it does not swell, but suffers erosion, 

 as it were, the solid mass of proteid being eaten out until finally only the indi- 

 gestible part remains, retaining the shape of the original mass, but falling into 

 fragments when shaken. In the second place, the hydrolytic cleavages seem 

 to be of a more intense nature. In peptic digestion, after the syntonin stage is 

 passed, there is a gradual change to peptone through the intermediate primary 

 and secondary proteoses. Under the influence of trypsin, according to the most 

 recent experiments, the solid proteid undergoes a transformation directly to 

 secondary proteoses (deutero-proteoses), the intermediate stages being skipped. 

 It was formerly thought that the solid proteid was converted first into a soluble 

 proteid, and that if the solution was alkaline some alkali-albumin was formed, 

 precipitable by neutralization, and comparable to the syntonin of pepsin-hydro- 

 chloric digestion. This soluble proteid was thought to be split into proteoses 

 of the hemi- and anti- groups which were then converted to the corresponding 

 peptones, according to Kiihne's schema (p. 231). There seems to be no doubt 

 that with the proteid most frequently used in artificial digestion namely ? 

 fibrin from coagulated blood the first effect is a conversion to a soluble 

 globulin-like form of proteid ; but Neumeister finds that this does not happen 

 with other proteids, and he thinks that in the case of fibrin it is not due to a 



