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succus entericus namely : (i) the mechanical distension of the intestinal 

 canal; and (2) the presence of pancreatic juice. He found that a flow 

 ot succus entericus could be more easily evoked by the introduction of a 

 small amount of fresh pancreatic juice into the intestine than by any 

 other means, and work by his pupils seems to point to the richness of the 

 juice in enterokinase being proportional to the amount of pancreatic juice 

 introduced into the canal. If these observations be correct, they would 

 point to the trypsinogen, or some associated substance in the pancreatic 

 juice, as being itself the chemical stimulant for the glands of the 

 intestinal wall. Whether this chemical irritant acts directly, or whether 

 it reaches the follicles of Lieberkiihn by way of the blood stream, is 

 as yet undetermined. Since it is the trypsinogen which needs the pre- 

 sence of enterokinase, it would be natural to assume that this substance 

 itself is the actual stimulant of the intestinal glands. 



A somewhat different view of the exciting agent for the intestinal 

 secretion has been put forward by Delezenne. This observer, working 

 on dogs with intestinal fistulas at various regions of the gut, obtained 

 practically no secretion except from the uppermost section namely, that 

 including the duodenum. He finds that the secretion of what we may call 

 duodenal juice, which must be succus entericus together with a small 

 amount of the secretion of Brunner's glands, is excited simultaneously 

 with the pancreatic juice and the bile by the injection of secretin into the 

 blood stream. According to this observer, therefore, the secretion of the 

 three cooperating juices in the upper part of the small intestine namely, 

 bile, pancreatic juice, and succus entericus containing enterokinase is 

 brought about by one and the same mechanism namely, the production 

 of secretin in the intestinal mucous membrane under the influence of the 

 entry of the gastric contents. It is, however, only in the upper part of the 

 gut that the chief role of the succus entericus can be regarded as adjuvant 

 to the pancreatic juice, and it is only here that the intestinal juice con- 

 tains any large quantity of enterokinase. Lower down in the gut a 

 secretion of alkaline intestinal juice is still of importance in consequence 

 of its content in (a) sodium carbonate for the neutralisation of the organic 

 acids produced in the changes in foodstuffs ; (b) the ferment erepsin which 

 breaks down the products of gastric and pancreatic digestion of proteids, 

 converting albumoses and peptones into the nitrogenous end-products, 

 amino-acids, and nitrogenous bases ; and (c) the ferments invertase and 

 maltase which complete the digestion of the carbohydrates of the food. 

 To these two ferments we must, in the case of milk-fed animals, add the 

 ferment lactase, in the absence of which milk sugar is incapable of 

 undergoing assimilation. 



According to Frouin the secretion of succus entericus (apparently in 

 the middle part of the small intestine) can be evoked by the intravenous 

 injection of succus entericus itself or by an extract of the intestinal mucous 

 membrane. It is difficult to see the teleological significance of such a 

 mechanism, unless we assume that some constituent of the succus enteri- 

 cus, produced by the mechanical stimulation of the foodstuffs themselves, 



