MOTHER CELLS AND DEDIFFERENTIATED CELLS 267 



accumulations " would seem to be of a similar nature, although 

 this is not as yet absolutely determined. 1 



Closely allied to this condition is what is seen in the lung, 

 and again in the serous coat of the peritoneum (though neither 

 of these, it is true, comes strictly under the category of true 

 gland structure). In the former, certain more embryonic cells 

 persist, especially at the angles of junction of the alveoli, and 

 these are generally regarded as centres for the normal proliferation 

 and regeneration of the alveolar epithelium. On the peritoneal 

 surface also there are found clumps of smaller cells capable of 

 active proliferation. With regard to both these cell layers, 

 the flattened — differentiated — cells are liable, under irritation, 

 to revert to the fuller, more rounded embryonic condition and 

 then undergo mitosis and proliferation. 



Judging from the fact that mitoses are not observed in the 

 fundal portions of several acinous glands, while they are frequent 

 in the neck regions of the same, it would seem at least probable 

 that mother cells, or cells capable of reverting to the mother cell 

 type, are situated in the latter area. But generally in acinous 

 glands of simple type there is, as Bizzozero has pointed out, little 

 evidence of continued proliferation under normal conditions, 

 once they are fully formed. In connexion with these it is 

 that more exact studies are requisite ; certainly in some, e.g. in 

 the kidney tubules, slight continued irritation leads to the 

 differentiated cells undergoing proliferation, but at the same 

 time these cells are seen to revert to the simpler, more embryonic 

 type. Thus, while confessing that it is not as yet possible to 

 demonstrate in every case that either mother cells are present 

 or that for regeneration the differentiated cells revert to a more 

 embryonic type, the number of examples that can be brought 

 forward, where either one or other of these processes is seen to 

 occur, is so large that we may assume that a general principle 

 obtains in connexion with all. 



Passing now to another tissue, namely muscle, the process of 

 regeneration, as pointed out by Barfurth, varies largely according 

 to the age of the individual. Originally the muscle fibres, it is 

 needless to say, are recognized as arising from a series of cells 



1 [Despite the abundant studies upon Langerhans's bodies which have been 

 made in the last seventeen years, the " mother cell " nature of these bodies is 

 still a subject of debate.] 



