ABSORPTION OF NUTRIMENT BY MUSSELS 421 



food is absorbed after being rendered soluble by the digestive 

 juices. In regard to the mechanism of the absorption of the 

 foods by the cells of the outer body walls little can be offered. 



In the case of the fats, numerous droplets which took the 

 Sudan III stain were found closely attached to the outer ends 

 of the epithelial cells of the gills or mantle. These droplets 

 were probably the fatty acids, a small part of which were pres- 

 ent in the soap solution owing to hydrolysis, by which process 

 sodium hydroxide and the fatty acids would be formed; the 

 remaining droplets were no doubt due to a slight acidity of the 

 surface of the living cells resulting from the union of carbon 

 dioxide from the cells with the water, forming carbonic acid. 

 In the experiments in which olive oil was saponified no attempt 

 was made to remove the glycerin from the mixtiu-e. There- 

 fore free fatty acids, from the droplets just mentioned, and 

 glycerin may have been absorbed separately and resynthesized 

 to fat within the cells. This absorption may have been effected 

 by phagocytic or amoeboid action of the cells or by solution in 

 the plasma membrane and reprecipitation within the cell. In 

 the case of the commercially prepared soap the objection might 

 be raised that there was no glycerin present to be absorbed and 

 reunite with the fatty acids after their entrance into the cells. 

 However it is safe to assume that a moderate amount of glycer- 

 in was present in the soap from the fact that in the process of 

 its manufacture the soap is 'salted out' of the glycerin, allowed 

 to rise to the surface and removed while wet with the glycerin. 

 Not all the glycerin is removed by the subsequent drying. 



Again it is not certain that the drops taking the osmic acid 

 stain as described in the author's preiious paper or the Sudan 

 III stain in the sections prepared by the freezing method were 

 fats or only the fatty acids. It is known that osmic acid blackens 

 or browns free fatty acids. It is possible that Sudan III also 

 stains them. At any rate solutions made from the commercially 

 prepared soap dissolve Sudan III readily and assume the char- 

 acteristic red color which that stain imparts to fat. It is prob- 

 able that both these stains for fat really affect the fatty acid 

 radical only and that it is that radical which carries the Sudan 



