•84 



iiErouT — 1884. 

 membrane has become thinner 



fi 



when the mucous membrane has become thinner owing to loss of the liniurr 

 epithelium in disease (as in cholera), althou}rh the coiiditimis are thereby rendered 

 more favourable for the osmotic prooesf, absorption from tlie interior of the 

 intestine is either much diminished, or the How is entirely in the opposite direction! 

 and tiiis in spite of the fact that the blood and lymph arc of more tlinn normiil 

 density. And, further, the osmotic theory has always failed to account foi' tliy 

 absorption of substances such as fat, which, aUhoufjrh tiuely subdivided, are Hdt 

 broup-ht into solution by the action of the digestive juices. In consequence of this 

 the absorption of fat has always been treated of as a subject quite distinct from 

 that of absorption of other nutritive matters, and has been explained by entiivjv 

 diflerent theories. Finally, no attempt has been made to explain how and wliere 

 the peptones which are formed in the alimentary canal are tniii.-:^forraed into the 

 proteids of the blood and lymph, although it is well known that these fluids contain 

 no peptones, so that the transformation must have occurred in tlio passage from 

 the intestine into them. 



I shall endeavour to show th.at the process of absorption from the intestine is 

 in all cases the same, and is not in all ^irobability a mere jrocess of osmosis, but 

 that it is effected by and through the activity of proto])lasm. If this is really the 

 case, the phenomena of intestinal absorption in the higher animals will be broujiht 

 into close eqiuvaleuce with the processes of absorption and assimilation which 

 occur in the simple Protozoa, with those of intercellular digestion which have been 

 observed in many of the lower Metazoa, and with processes of physiological and 

 pathological absorption of tissues which occur in higher animals. 



In studying ' phases of absorption it is convenient to employ fats as a pnrt 

 at least of the met, because of their property of lieconiiiig stained darkly by 

 osmic acid. In most of my experiments therefore the animal has been ted, ii 

 certain time before being killed, with food containing fat, and immediately after 

 death minute portions of the mucous membrane of the small intestine have been 

 placed in osmic acid or in a mixture of chromic and osmic acid. These fluids 

 instantly iix the tissues, and stain the fat globules in them. 



I have always found at a certain period after ingestion of food, the period 

 varying in different animals and in different portions of the small intestine, fat in 

 great abundance in the columnar epithelium cells. The fact of its occurrence in 

 them is so well known and so easy to circumstantiate that one is surprised to find 

 it ignored by some eminent histologists. The fat globules occnr first of all in the 

 part of the protoplasm nearest the cuticular surface of the cell ; later they are 

 found also on the other side of the nucleus, and here most generally in a more 

 finely divided condition. Examined still later, fat globules, generally very fine. 

 are seen in large numbers in the leucocytes which are so abundant in the retiform 

 tissue of the villi and mucous membrane generally, and which extend also between 

 the epithelium cells. And, finally, the lacteal in the centre of each villus is found 

 to contain similar fine tatty globules in large amount. I have not been able to 

 find any evidence, either in teased preparations or in sections, of the presence of 

 fat in the network of the retiform tissue, but only in the epithelium cells, the 

 leucocytes, and the central lacteal. 



So far the facts which I have here mentioned are not new, for they were 

 announced already in the 8th edition of Quain's ' Anatomy,' and in my 'Course of 

 Practical Histology,' published in 1876. And the conclusion which I was led to 

 draw from them, and which seems to me to be inevitable, is that in the absorption 

 of fut, the finely divided fat particles are taken up from the intestinal contents by 

 the columnar epitlielium cells, are by them passed on to the leucocytes which Lave 

 wandered between those cells, and are by the leucocytes carried, by virtue of their 

 amoeboid movements, to the central lacteal, where the cargo of absorbed fat is 

 discharged. I was unable at the time to determine how this discharge of the fat 

 particles is eftiected, nor whether the same leucocytes may pass back again to the 

 epithelium, and serve to carry a fresh cargo. 



More recently, however, in continuing these and other researches bearing upon 

 the functions and properties of the white blood corpuscles and similar cells, I 

 have come across another fact which fully elucidates this problem, and whicb 



