CHAP. iv. ISOLATION OF FAT IN VILLI AND ALVEOLI. 285 



finely divided fat does pass from the intestine, through the epithelial 

 cells which envelope the villus, and so into the channel of the lacteal. 

 Most observers agree that after a meal the epithelium cells of the villus 

 are gorged with fat, the particles of which must have entered the cells 

 very much as foreign particles enter the body of an amoeba. The cells 

 may thus be said to eat the fat, and subsequently to pass it on in the 

 direction of the channel of the lacteal. There would thus be a stream 

 of fatty particles through the cell, a stream in the causation of which 

 the cell took an active part. In fact, under this view, absorption by 

 the cell might be regarded as a sort of inverted secretion, the cell 

 taking much material from the chyme and secreting it with little or no 

 change into the villus. 1 



Professor E. A. Schafer has actually demonstrated in his paper, 

 " On the origin of the proteids of the circle and the transference of 

 food materials from the intestine into the lacteals," 2 that lymph cor- 

 puscles play an important part as carriers of fat into the lacteals of the 

 villi. They take up, amoeba-fashion, the fatty particles from the epi- 

 thelium cells of the villi, and thus* fat-laden they wander towards the 

 centre of the villus and enter the lacteal, inside which the coat of the 

 migratory lymph cell is dissolved and its contained fat set free. It is 

 particularly worthy of note that migratory or lymph corpuscles occur 

 in the tissue between the alveoli of the mammary gland. 



Considerations such as the foregoing lead to the splendid generalisa- 

 tion that the epithelial cells of the villi, the secreting cells of the mam- 

 mary gland, and the colourless corpuscles of the blood, may be regarded 

 as amoebae, that, in fact, the whole animal body may be viewed as 

 groups of amoebae, associated together for man} 7 and varied objects, the 

 different groups exhibiting specialisation of structure in accordance 

 with the nature of the work they are respectively called upon to per- 

 form, the functions of one group differing from those of another in 

 conformity with the strict physiological division of labour which is an 

 inevitable condition of existence, if the aggregation of cells is to 

 exhibit any characters of a higher order than those which belong to 

 the cell as an individual. 



A comparison of the epithelial cells of the villus with those of the 

 alveoli of the mammary gland seems to bring under notice a similarity 

 of behaviour with respect to the disposal of the particles of fat with 

 which they, in each case, become laden. In the former case the 

 globules are ejected into the interior of the villus ; in the latter case, 

 they are ejected into the cavity (or lumen, as it is called) of the 

 alveolus, and in both cases the mechanical action is comparable with 

 that whereby an amoeba ejects from its body such matters as it has no 

 further use for. In all other respects, however, the epithelial cells 

 of the mammary gland possess functions of a far more exalted 

 order than those of the epithelial cells of the villi, for the former 

 actually manufacture the fat they contain out of the blood they 



1 Foster, "Physiology." 



2 "Proc. Roy.'Soc./' No. 235, 1885. 



