FROM THE SMALL INTESTINE 643 



peristalsis of the gut within a minute of being painted on its 

 peritoneal surface. He found that Ca salts applied locally would 

 prevent the peristalsis, just as Loeb had found that Ca salts can 

 stop contact irritability of muscle and the hyper-sensitiveness 

 of the nervous system induced by various salts. MacCallum 

 showed further that besides inducing peristalsis these purgatives 

 may increase the normal secretion of the intestinal glands ten- 

 fold, and that this effect as well as the normal secretion may be 

 inhibited by Ca salts. We may therefore conclude that solu- 

 tions of the saline purgatives are slowly absorbed, but that the 

 portion which is absorbed rapidly leads to an increased secretion 

 of fluid from the intestinal glands, and that consequently the 

 quantity of fluid obtained from the gut at the end of an ex- 

 periment is not an accurate measure of how much of the original 

 solution remains unabsorbed. MacCallum has also shown that 

 when large quantities of NaCl solution isotonic with the plasma 

 are injected intravenously, there is a rapid secretion into the 

 intestine of fluid containing -25 per cent, dextrose. When we 

 recollect Colenheim's experiments on the absorption of dextrose 

 with an artificial circulation of NaCl solution, MacCallum's results 

 emphasise the impression that in the present state of our know- 

 ledge solutions of electrolytes are unsuitable for investigating 

 the mechanism of intestinal absorption. 



The Path of Absorption. It has frequently been assumed that 

 all material is absorbed through the epithelial" cells. But the 

 epithelial layer consists of cement substance as well as cells ; it 

 is therefore possible that material might pass through the cement 

 substance by a physical process, and that such material as 

 passed through the cells might be transported by their vital 

 activity. Our knowledge of the actual path taken by different 

 substances is extremely meagre. We know that the products 

 of fat digestion pass into the epithelial cells, but we know 

 nothing of the path taken by the products of proteid and carbo- 

 hydrate digestion. Heidenhain placed solutions of methylene- 

 blue in the intestine, and found two hours later the dye both 

 within and between the cells. From this he concluded that 

 water can be absorbed by both routes. MacCallum has definitely 

 shown that iron salts can pass into the epithelial cells. He 

 does not discuss the possibility of their passing between the cells 

 as well; but, from the fact that he sometimes found none in 



