OBSERVATIONS ON STRUCTURE OF CELLS AND NUCLEI. 133 



contract and expand, and thereby to change the relation between 

 the thickness of the whole epithelial lining and the size of the 

 lumen, as Engelmann found it to be the case in the small glands of 

 the nictatory membrane of frog, I am not in a position to affirm 

 or to deny. But there seems to be one fact that might be taken 

 as pointing towards a similar relation as that in Engelmann^s case, 

 viz. the fact that there are a good many crypts in which, without 

 any formed matter being found in the lumen, this latter (lumen) 

 is more or less distended, and the lining epithelial cells propor- 

 tionately shortened. This, however, admits also of another ^plana- 

 tion, which will appear later on in connection with the submaxil- 

 lary and other glands. The longer the epithehal cells the more 

 distinct do they show the longitudinal arrangement of the fibrils 

 of the intercellular network. 



This change of the shape of the epithelial cells under different 

 conditions is a subject which does not seem to me to have 

 received sufficient attention yet. I shall have occasion in another 

 paper to describe in detail my observations with regard to this 

 subject, but I wish only here to mention a few facts necessary 

 for the interpretation of the above appearances. I have shown ^ 

 that the endothelium covering the pulmonary pleura changes its 

 shape during the respiratory movements of the lung, inasmuch 

 as the individual endothelial plates become flattened during the 

 maximum of inspiration, and return again to their previous shape 

 during expiration. Kiittner ~ has shown that with the first 

 inspiration the epithelial cells lining the alveoli of the lung change 

 from columnar cells into flat cells, and this shape they retain in 

 the post-foctal lung. But I have convinced myself that also in 

 the adult during respiration some epithelial cells of the air- 

 vesicles and also of the bronchi undergo a change of shape. 

 As is known since Elenz and others, the lining of the alveoli of 

 most mammals — especially cat — contain amongst the ordinary 

 flat epithelial cells small cubical cells arranged singly or in groups. 

 ¥. E. Schultze ^ has very carefully described and figured these 

 appearances. 



I find that those air-vesicles of lung of cat that are in a state 

 of expansion, such as is the case in a deep inspiration, possess 

 very few of these small epithehal cells amongst the ordinary 

 flat ones, their number being considerably greater if the air- 

 vesicles are contracted, such as is the case in a deep expiration. 

 These small cubical cells appear to be more " granular " than the 

 other large flat cells, which are more or less hyaline. I am, 



1 ' Anatomy of the Lymphatic System,' ii, Part 1, " The Lungs," p. 2, 



2 Virchow's ' Archiv,' Band Ixvi, p. 12, ei passim. 



* Strieker's ' Handbook of Histology/ chapter " Tlie Lung." 



