THE LIVER AND PANCREAS 257 



As free fatty acids, soaps, and glycerine, the fat enters the 

 villus and gains the chyle vessel. At one time it was believed 

 fat in fine emulsion passed between the epithelial cells of the 

 villus, but this is now known to be wrong. The oil globules seen 

 in the villus represent the newly reconstructed fat, for the 

 soluble products of fatty acids, soaps, and glycerine have no 

 sooner got into the villus than neutral fat is reconstructed. 

 Some think this is brought about by the reversible action of 

 lipase, others believe the effect is due to the living cells of the 

 villus, and not the result of the action of a ferment. No further 

 change occurs to the fat until it reaches the blood. Oil globules 

 in the blood would not pass along the capillaries, and plugging of 

 the vessels would occur. This is prevented by a change brought 

 about in the blood, by which the fat is rendered soluble, dialys- 

 able, and capable of passing through the capillary wall. The 

 method by which the blood effects this change is unknown ; it 

 is said, however, that lipase may be found in the blood, muscles, 

 liver, and other glands, and if so this will account for fat embolism 

 not occurring in the vessels, and also explains why the tissues 

 are able to draw on their body fat as required, for this must be 

 brought into solution before it can pass back into the blood. 



Lipase is readily destroyed, so that unless quite fresh it does 

 not do its work in artificial digestions. It is believed that a 

 portion of the lipase is secreted in the inactive condition as 

 a zymogen, or pro-enzyme form, and that this is activated by the 

 action of the bile acids and lecithin. Whether this is so or not, 

 the dependence of the pancreatic secretion on the good will of the 

 bile is a very important matter. 



On p. 188 we have alluded to Pawlow's work on the quantity 

 and quality of the gastric juice being regulated by a specific 

 action on the part of the food itself. Similarly, the same observer 

 has shown that the ferment contents of the pancreatic juice are 

 adapted to the character of the food ; for example, the lipase is 

 increased by a fat diet. A definite and unchanging diet leads to 

 the formation of a pancreatic juice, which is unable to deal effec- 

 tively with a sudden change in food. The practical bearing of 

 this in the feeding of animals is far-reaching. As a profession we 

 have recognised for years the disastrous effects of sudden 

 changes in diet ; modern science offers the explanation of its 

 action. The whole matter is probably regulated by an internal 

 secretion. 



The Changes occurring in the Cells of the gland correspond 

 very closely with those described for the salivary secretion. 



When a pancreas or lobe of a pancreas has been at rest for 

 some time the cells forming it are rendered very indistinct ; the 

 lumen of the alveolus is nearly obliterated by their swollen 



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