ALVEOLI OF THE SALIVARY GLANDS. 425 



be brought into unison with it. Thus, (1) on examination of 

 the membrana propria in fresh preparations, I have never been 

 able to distinguish a nucleus, although I tested for it with 

 dilute chromic acid, which causes the nuclei of the epithelial 

 cells to come into prominent relief, and although the quadri- 

 polar flattened cells regarded by Boll and Kolliker as consti- 

 tuents of the membrana propria frequently contain a very 

 brilliant large nucleus, which, according to Boll, may be round 

 and very thick. (2) The vesicular elevation of the membrana 

 propria from the salivary cells, consequent upon diffusion, pre- 

 supposes a continuous membrane, which in fact comes into 

 view, whilst it is impossible to see any reticulum. (3) The small 

 quadripolar cells of the reticulum so rarely occur in rabbits 

 that they are by no means sufficient to furnish an investment 

 to all the alveoli. (4) The quadripolar cells are unquestionably 

 connected with the epithelial cells by means of processes, and 

 cannot consequently be regarded as connective tissue cells, 

 a point, into the consideration of which it will be hereafter 

 necessary to enter. The view entertained by Boll and Kolliker 

 has not, consequently, at present received adequate confir- 

 mation. 



In the next place, as regards the contents of the alveoli. 

 These consist of cells filled with numerous granules, so that 

 the gland substance appears black by transmitted light, ren- 

 dering it impossible to distinguish either the cell contour lines 

 or the nuclei. Such are the appearances presented by perfectly 

 fresh preparations made from the gland whilst still warm 

 and almost living, if moistened with the aqueous humour. 

 In diluted chromic acid, containing one-fiftieth per cent., the 

 greater part of the granules quickly dissolve, whilst the alveolus 

 becomes transparent, and presents the most beautiful mosaic 

 of cells. For this experiment the submaxillary glands of the 

 rabbit are admirably adapted. Every cell is rendered polygonal 

 by mutual compression, and presents sharply defined bright 

 double contours. For the most part they only form a single 

 layer, which lines the central canal of the gland, and is diffe- 

 rentiated from this by a sharp contour line. In most animals 

 the membrana propria is easily elevated. The cells adhere very 

 strongly to one another, so that after being detached from the 



