832 PHYSIOLOGY 



balanced by the increased osmotic pressure, or attraction for water, 

 of the intestinal contents. 



Cushny and Wallace, as the result of their experiments on the relative absorb- 

 ability of salt solutions from the gut, divide the salts into four main classes as 

 follows : 



I II III IV 



Sodium chloride, Ethyl sulphate, Sulphate, phosphate, Oxalate, 



bromide, iodide, nitrate, lactate, sali- ferrocyanide, capry- fluoride, 



formate, acetate, cylate, phthallate. late, malonate, succi- 



propionate, butyrate, nate, malate, citrate, 



valerianate, caprate. tartrate. 



Of these the first class contains those salts which are absorbed with great 

 ease from the intestine. The second group of salts are absorbed with somewhat 

 greater difficulty. The third group are absorbed so slowly, i.e. the salts retain 

 the water in which they are dissolved so long, that they increase peristalsis and 

 act as laxatives or purgatives. The members of the fourth class are not absorbed 

 at all. It is evident that this classification is independent of the diffusibility 

 of the salts. Sodium acetate has a much smaller dissociation value and a lower 

 diffusibility than sodium chloride or iodide, and yet is absorbed at approximately 

 the same rate as these two salts. There is, however, as Cushny pointed out, 

 one physical or chemical character which apparently deternu'nes the non-absorb- 

 ability (relative or absolute) of the members of the third and fourth classes. 

 All these salts form insoluble compounds with calcium. This common 

 character is not an explanation of the permeability of the cell wall, but is simply 

 a general statement of one of the conditions which affect the power of the cells 

 to take up salts from their solutions, this power being absent in the case of salts 

 which furnish an insoluble calcium compound. 



THE ABSORPTION OF FATS 



Fats administered to an animal in excess of its diurnal require- 

 ments are stored up in the body in the form in which they are 

 administered. Each cell of the body probably possesses in itself the 

 mechanism for the utilisation of these neutral fats, and for effecting 

 in them the various changes involved in the successive stages of their 

 disintegration and oxidation through which they are finally converted 

 to C0 2 and water. The problem therefore of fat absorption is 

 ultimately one of the simplest with which we have to deal, and 

 involves merely the transference of the neutral fat of the food to 

 the circulating fluids in such a form that it can be carried by them 

 to the place where it is required for the metabolism of the body or 

 where it may be stored up as a reserve substance. 



The processes of digestion of fat result in the production of glycerin 

 and fatty acids, if the reaction be neutral or slightly acid. If the 

 reaction of the gut be alkaline the alkali will combine with the fatty 

 acids to produce soaps. Analyses of the contents of the gut after 

 a fatty meal show that the greater proportion of the fats are present 



