CH. xxxiv.] ABSORPTION OK FATS. 517 



at the end of a given time the contents of the loop were again analysed. 

 The pressure in the loop and in the mesenteric veins was estimated mano- 

 metrically during the progress of the experiment : allowance was made for 

 the secretion of intestinal juice, and other precautions taken to make each 

 experiment as complete as possible. 



It was found that the absorption by an animal of its own serum or plasma 

 takes place under conditions in which filtration or osmosis into blood 

 capillaries or laeteals and also adsorption (or imbibition) are excluded. 

 The active force must therefore by a process of exclusion reside in the 

 physiological activity of the lining epithelium. The same conclusion was 

 reached by another method, namely, that when the epithelium is removed, 

 injured or poisoned, the absorption either ceases or is markedly lessened, 

 and this in spite of the fact that removal of the epithelium must increase 

 the facilities for osmosis and filtration. 



The activity of the cells is characterised by a slower uptake of the organic 

 solids of the serum than of water, and a quicker uptake of the salts than of 

 the water : but the absolute numerical relations varies in different regions 

 of the intestine. The state of nutrition of the cells is the main factor in 

 their activity ; s|>ecinc absorptive nerve-fibres were sought for but not found. 

 The absorption of water from the gut depends partly on the physical 

 relation of the osmotic pressure of the solution in the intestine to that of 

 the blood plasma ; but even the absorption of water is influenced by the 

 physiological regulation of this difference by the directing or, as it may be 

 termed, orienting mechanism of the cells. Such orienting action was first 

 noted in connection with salts by Otto Cohnheim ; he showed that, in an 

 intestinal loop witli injured cells, sodium chloride enters its lumen from the 

 blood though the same salt is l>eing actively absorbed from a normal loop in 

 the same animal at the same time. In all probability the cell activity which 

 causes the organic constituents of serum to pass into the blood is of the same 

 nmture as that involved in the orienting action of the cells upon salts in 

 solution. 



Professor Reid's conclusions with regard to the absorption of peptone and 

 sugar are as follows : The chief factor in the absorption of peptone is an 

 assimilation (or adsorption) by the cells, while in the absorption of glucose 

 diffusion variable by the permeability of the cells (and so probably related 

 to their physiological condition) is the main factor. By removal of the 

 epithelium the normal ratio of peptone to glucose absorption is upset, and 

 the value tends to approach that of diffusion of these substances through 

 parehinent paper into serum. Differences are also noted in different parts 

 of the intestinal canal. 



Tin- still more wonderful synthetic power which the cells exercise in 

 n-lation to proteids and fats has been already mentioned in the main text. 



The fseces arc alkaline in reaction, and contain the following 

 substances : 



1. Water: in health from 68 to 82 per cent. ; in diarrhoea it 

 is more abundant still. 



2. Undigested food : that is, if food is taken in excess, some 

 escapes the action of the digestive juices. On a moderate diet 

 unaltered proteid is never found. 



3. Indigestible constituents of the food : cellulose, keratin, 

 mucin, chlorophyll, gums, resins, cholesterin. 



4. Constituents digestible with difficulty : uncooked starch, 

 tendons, elastin, various phosphates, and other salts of the alkaline 

 earths. 



