v INTEENAL EESTITUTIVE SECEETIONS 279 



of glycerol, and then treating the intestinal epithelium with 

 osmic acid, the same microscopic results were obtained as after 

 feeding with neutral fats. Will observed the same thing, even 

 when the frog is fed with fats of such a high melting-point, that 

 they cannot be liquefied and emulsified in the intestine. Ewald 

 made the same observations on the intestinal epithelium in 1883, 

 after stripping off the mucous coat of the intestine, and setting it 

 to digest at body-temperature in a solution of soaps and glycerol. 

 This shows that synthesis of the fatty acids and glycerol may be 

 effected by the epithelial cells which survive the separation from 

 the body. 



On the other hand, we know from countless observations, 

 particularly those of Cash, in Ludwig's laboratory (1881), of 

 I. Munk (1885), and Heidenhain (1888), that the intestinal chyme 

 of the dog is almost always acid from the pylorus to the ileo-caecal 

 valve, and that consequently the fat which it contains is not 

 emulsified, or at any rate only imperfectly so, and exhibits drops 

 of fat many times coarser than those observed under the microscope 

 in a true emulsion. And yet, Munk says expressly, it can be 

 seen in the parts of the small intestine in which the chyme is 

 acid, and in which the non-emulsified fat floats here and there in 

 large drops, that the lymphatics of the mesentery are full of 

 milky chyle, a proof that fat absorption is going on, even when 

 it is not emulsified and when the chyme has an acid reaction. 

 This observation proves that the fat is absorbed under another 

 form, perhaps in that of fatty acids or of soaps. In fact, when 

 soaps or fatty acids are fed to a dog, small fractions only reappear 

 in the faeces, if fatty acids with a low melting-point are taken. 



On analysing the chyle resulting from these experiments, it is 

 found to contain a large quantity of neutral fats, while the 

 content of free fatty acids and soaps has hardly increased at all, 

 and is very insignificant. This fact agrees perfectly with the 

 theory which admits that the fats, like all other food-stuffs, are 

 absorbed in the form of solutions, i.e. after cleavage, and are 

 synthetically regenerated after penetrating the cytoplasm of the 

 epithelial cells. 



Other more direct arguments in favour of this theory are 

 furnished by microscopical observations of the intestinal epithelia 

 in successive phases of fat absorption. All who have occupied 

 themselves with this subject (Kolliker, Will, Ewald, Eimer, 

 Eanvier, and others) agree in admitting that certain parts of the 

 columnar cell and the whole of the striated border, in particular, 

 are always quite free of fat-drops. 



The results obtained by Altmann (1889) and his pupil Krehl 

 (1890) are more decisive. If osmic preparations of the frog's 

 intestinal epithelium are studied in various stages of fat absorption, 

 the cytoplasm is seen to be full of granules, the size of which 



