720 PHYSIOLOGY 



ensured by one and the same mechanism, namely, by the simultaneous 

 activity of the secretin, produced in the intestinal cells by the action of 

 the acid chyme, on pancreas, liver, and intestinal glands. A further 

 chemical mechanism for the arousing of intestinal secretion has been de- 

 scribed by Frouin. According to this observer, the flow of juice can be excited 

 by intravenous injection of intestinal juice itself. Since this juice is alkaline, 

 and does not produce any effect on the pancreas, it must be free from pan- 

 creatic secretin. It would seem therefore that the flow of juice in the upper 

 part of the gut, excited by the pancreatic secretin, causes also a production of 

 a different secretin or hormone, which can be absorbed from the lumen of the 

 gut, travel by the blood stream to other segments of the small intestine, and 

 there excite a secretion in preparation for the on-coming food. Further 

 experiments are, however, necessary on this point. 



The glands of the small intestine can also be excited by direct mechanical 

 stimulation of the mucous membrane. The easiest method of exciting a 

 flow of intestinal juice from a permanent fistula is to introduce into the 

 intestine a rubber tube. The presence of the solid object in the gut causes 

 a secretion, and within a few minutes drops of juice can be obtained from 

 the free end of the tube. The object of such a sensibility to mechanical 

 stimuli is obvious ; it is of the highest importance that the onward passage 

 of any solid object, especially if it be indigestible, shall be aided by the 

 further secretion of juice in the portions of gut which are immediately 

 stimulated. This mechanical stimulation probably acts on the tubular 

 glands of the intestine through the intermediation of the local nervous 

 system, the plexus of Meissner. It is stated by Pawlow that a juice obtained 

 by mechanical stimulation differs from that produced by the introduction of 

 pancreatic juice into the loop in containing little or no enterokinase, so that 

 the pancreatic juice excites the secretion of the substance which is necessary 

 for its own activation. 



CHARACTERS OF INTESTINAL JUICE 



The intestinal juice obtained from a permanent fistula has a specific 

 gravity of about 1010. It is generally turbid from the presence in it of 

 migrated leucocytes and disintegrated epithelial cells. It contains about 

 1*5 per cent, total solids, of which 0-8 per cent, are inorganic and consist 

 chiefly of sodium carbonate and sodium chloride. It is markedly alkaline in 

 reaction, but less so than the pancreatic juice. The organic matter, besides 

 a small amount of serum albumin and serum globulin, includes a number of 

 ferments, all of which are adapted to complete the processes of digestion 

 of the food- stuffs commenced in the stomach and duodenum. Of these 

 ferments two are concerned in proteolysis. Enterokinase we have already 

 studied in detail. Possessing no action itself on proteins, it is a necessary 

 condition for the development of the full proteolytic powers of the pancreatic 

 juice. In addition to this ferment another ferment has been described by 

 Cohnheim under the name ' erepsin.' Erepsin or some similar ferment is 

 present in the fresh pancreatic juice and in almost all tissues of the body. It 



