

DIGESTION 129 



of the intestine is not a membrane. The cells which line the 

 intestine take up substances far less easily diffusible than the 

 sulphate of magnesia which they refuse. Nevertheless, speak- 

 ing generally, it is the less diffusible salts which act as aperients, 

 the more diffusible which are absorbed. The forward passage 

 of the contents of the alimentary canal is hastened by castor-oil. 

 The peristalsis of the intestines is stimulated by certain drugs, 

 such as jalap or the burnt products of tobacco. Another class 

 of drugs, of which aloes is an example, increases the secretion 

 of the intestines, small or large. Certain purgatives, such as 

 calomel, podophyllin, etc., used to be regarded as cholagogues. 

 It was supposed that they increased the flow of bile. This is 

 an error. Their action is complicated, but it affects chiefly 

 the peristalsis of the intestine. The poor misunderstood liver 

 still suffers from the libels of primitive medical science. It is 

 the most innocent of organs, in no way responsible for derange- 

 ments of digestion. It carries out its functions without haste 

 and without delay. With the possible exception of salicylate 

 of soda, no drug is known which can stimulate it to a more 

 rapid output of bile. 



Absorption. All the cells which line the alimentary canal 

 are capable of absorbing food, if it is presented to them in a 

 suitable form. In a suitable form means, speaking generally, 

 in a diffusible condition, although it must not be supposed that 

 the epithelial cells are incapable, under certain circumstances, 

 of taking up non-diffusible substances, just as a unicellular 

 organism an amoeba can take in food. If soluble proteins, 

 such as white of egg or acid-albumin, are injected into the large 



serum inside the intestine and the lymph on the outside. There would be 

 no osmosis. Or, again, supposing water containing 2 % of common salt is 

 placed in the intestine, we find that both salt and water pass through into 

 the lymph. In a dialyser water would pass from the lymph (which contains 

 salts equal to about 0*9 % of sodic chloride) through the membrane into the 

 stronger solution. A salt-solution needs to be very concentrated to cause 

 water to take the reverse course through the intestinal wall, and so to act as 

 a purgative. When we study absorption from the alimentary canal, we find 

 that its wall, if it wants a salt or any other substance, sets the laws of osmosis 

 at defiance. If the salt is not wanted, the ordinary phenomena of osmosis 

 are exhibited. 8ulphate of magnesia (Epsom salt) would be deleterious if 

 absorbed. The intestinal wall behaves towards it like a dead membrane. 

 The salt retains the water in which it is dissolved : possibly water passes 

 out of the lymph into the solution of the salt. The contents of the intestines 

 are in consequence unduly liquid. The salt acts as a purge. 



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