GLANDULAR CELLS OF THE FROG'S PANCREAS 359 



The process of adhesion may proceed to varying extents according 

 to the nature of the fixatives, the success or failure of fixation, 

 the stage of cell function, and other unknown causes, thus leading 

 to the formation of many enigmatic structures, as have been de- 

 scribed by various investigators. 



As above mentioned, the fixatives such as alcohol, trichloracetic 

 acid, formalin, bichromate-formalin, etc., cause only slight adhe- 

 sion of protofibrillae, so that, in such cases, parallel striation 

 or only a slight sign of net formation at most is produced (figs. 48 

 to 52). In fixatives like Carnoy's, Zenker's, sublimate-acetic, 

 bichromate-acetic mixture, etc., on the contrary, the changes are 

 much more pronounced; this is especially true of the deeper 

 parts of the block where the cell is ordinarily poorly preserved. 

 There are a great many variations in the degree of adhesion. 

 Either fiber-bundles, or a network situated in the basal portion 

 of the cell-body may be formed, as seen in figures 36 to 38, 110, 

 118. On the other hand comma-, crescent-, or shell-like struc- 

 tures (figs. 40, 84) may be formed by the adhesion of a large 

 number of fibrillae and then applied either to one side of the 

 nucleus or to the cell periphery. Finally, smaller or larger 

 spherical corpuscles may be formed by the agglomeration of the 

 fibers and show more or less pronounced concentric striation (figs. 

 37, 39, 84, 100, 101, 105). There are all grades of transition be- 

 tween mere striation and agglomeration of the fibers, and it often 

 happens that not only the different cells, but also one and the 

 same cell contains different types of structures. It must also be 

 here noticed that the structures formed by the adhesion of 

 a large number of fibers, such as thick bundles, commas, or 

 crescents, etc., generally stain more deeply with haematoxylin, 

 which is perhaps due to their compact character in consequence 

 of the close apposition of the constituting fibrillae. 



From the above description it is evident that a large amount 

 of acetic acid in fixatives produces remarkable adhesion of the 

 fibrillae; yet the 'superficial cells, even in such fixatives as bi- 

 chromate-acetic or sublimate-acetic mixture, are fairly well pre- 

 served, so that there occurs only slight adhesion (figs. 80, 81) or 

 none at all. This discrepancy can perhaps be explained by the 



