490 



DIGESTION IN THE INTESTINES. [CH. xxxil. 



or fats is very doubtful ; its most important action is due to a 

 ferment it contains called invertin, which inverts saccharoses 

 that is, it converts cane sugar and maltose into glucose. 



The original use of the term " inversion " has been explained 

 on p 387. It may be extended to include the similar hydrolysis 

 of other saccharoses, although there may be no formation of 

 levo-rotatory substances. There are probably numerous inverting 

 ferments, each of which acts on a different saccharose. 



Succus entericus has been obtained free from other secretions by means of 

 a fistula. Thiry's method is to cut the intestine across in two places ; the 

 loop so cut out is still supplied with blood and nerves, as its mesentery is 



II 



Fig. 401. Diagram of intestinal fistula. I., Thiry's method; II., Vella's method. A, 

 abdominal wall ; B, intestine with mesentery ; C, separated loop of intestine, with 

 attached mesentery. 



intact ; this loop is emptied, one end is sewn up, and the other stitched to 

 the abdominal wound, and so a cul-de-sac from which the secretion can be 

 collected is made. The continuity of the remainder of the intestine is 

 restored by fastening together the upper and lower portions of the bowel 

 from which the loop has been removed. Vella's method resembles Thiry's 

 except that both ends of the loop are sutured to the wound in the abdomen. 

 Fig. 401 illustrates the two methods. 



Bacterial action. The gastric juice is an antiseptic ; the 

 pancreatic juice is not. A feebly-alkaline fluid like pancreatic 

 juice is just the most suitable medium for bacteria to flourish in. 

 Even in an artificial digestion the fluid is very soon putrid, unless 

 special precautions to exclude or kill bacteria are taken. It is 

 often difficult to say where pancreatic action ends and bacterial 

 action begins, as many of the bacteria that grow in the intestinal 

 contents, having reached that situation in spite of the gastric 

 juice, act in the same way as the pancreatic juice. Some form sugar 

 from starch, others peptone, leucine, and tyrosine from proteids, 



