404 PRACTICAL PHYSIOLOGY 



has no action, and that it can carry hydrolysis to a further stage than 

 trypsin. Like trypsin, it acts best in alkaline reaction. It is more 

 plentiful in extracts of intestinal mucous membrane than in succus 

 entericus. It is probably, therefore, an intracellular ferment endoen- 

 zyme some of it leaking out of the cells into the succus entericus. 

 Since the proteins (i.e. peptones) have to pass through these cells during 

 absorption, they will come under the influence of erepsin. Erepsin is 

 not confined to the intestine, but is present in large amount in other 

 parts of the animal body. Next to the intestine, the largest amount 

 has been found (by Vernon) in the kidney, then, in order, the spleen, 

 pancreas, liver, cardiac muscle, brain, skeletal muscle, serum. These 

 endo-erepsins of the tissues probably play an important role in the 

 metabolism of proteins. 



ADVANCED EXPERIMENT. To Demonstrate the Breptic Power of Tissues. 

 Take 20 grm. minced liver, and 20 grm. mucous membrane of the intestine 

 (scraped off with a scalpel). Grind each in a mortar with fine quartz sand and 

 20 c.c. of a 0'2 % solution of Na 2 Co 3 . Filter the extracts through muslin. Divide 

 each extract into two equal parts, A and B. To A of each extract add 1 c.c. of a 

 2'5 % solution of Witte's peptone, and to B a similar amount of a 2'5 % solution 

 of egg-white. Remove a few drops of the contents of each of the four test tubes, 

 and apply the Biuret test, noting the results. Place the tubes in the incubator 

 at body temperature, and at the end of an hour again remove a little of the 

 contents of each tube, and apply the Biuret test. It will be found that there 

 is no change in the tube (B) containing egg-white, but that in the tube (A), 

 containing the intestinal extract, the test has become very feeble or disappeared 

 entirely. By longer incubation, the Biuret secretion will also disappear from 

 the tube (A) containing liver. 



By thus ascertaining the time required to split up a standard solution of 

 peptone, so that the Biuret test is no longer given, a comparative estimate may be 

 made of the ereptic power of different extracts. 



Another ferment-like body in succus entericus is enterokinase. Alone, 

 it has no action on any food- stuff, but when mixed with trypsinogen it 

 converts it into trypsin. On a flesh-free diet, the pancreatic juice, as 

 secreted from the duct of Wirsung, contains very little trypsin, and 

 digests coagulated egg-white only slightly even after several hours. If 

 to this inactive pancreatic juice a few drops of succus entericus be 

 added, digestion of the egg-white proceeds actively. Trypsinogen, 

 which is the form in which the proteolytic ferment is secreted on a 

 flesh-free diet, remains inactive until it gets to the intestine, where 

 it is converted into trypsin by the entero-kinase. Enterokinase is 

 not secreted unless it is required, i.e. if the intestinal mucosa be 

 mechanically stimulated, a juice will be secreted which contains no 

 entero-kinase. 



Bacterial Digestion. As has been explained above, the conditions 



