GLANDULAR CELLS OF THE FROG'S PANCREAS 357 



structures of the cytoplasm brought about by the accumulation 

 of zymogen granules bear no relation to the proper construction 

 of the plasm. We know, on the one hand, from daily experience, 

 that the plasm exhibits extraordinary diversity of structure ac- 

 cording to the nature of fixatives, and that, therefore, it would 

 be premature to draw any conclusion from such observations; 

 and, on the other hand, one searches in vain, in most cases, for 

 minute structures of the cytoplasm as studied in the fresh condi- 

 tion, since the cytoplasm then appears perfectly homogeneous 

 except for some ill-defined granules or filaments. It would also 

 be rash, from this, to conclude that the cytoplasm is entirely 

 devoid of structure. It is, for the present, indispensable to the 

 study of the plasm to allow various fixatives to act upon the 

 cytoplasm and to compare the structural changes so produeed 

 with one another. In fact, some of the fixatives act in such a 

 way that the plasm is as well preserved as seen in the fresh state; 

 others cause so pronounced changes as often to lead to the forma- 

 tion of very fantastic structures. There are many gradations 

 of the action of fixatives between these two extremes. 



In general, osmic or chromic acid mixtures containing a very 

 small amount of acetic acid or without this, such as Altmann's, 

 Benda's, or Meves,' fix in such a manner that the protoplasm 

 proper of the pancreatic cell, provided the fixatives acted with 

 sufficient power upon the plasma, shows no structural particu- 

 larities (figs. 44 to 47, 55, etc.). On the contrary, the fixatives 

 which contain a larger amount of acetic acid, such as Zenker's, 

 Carnoy's, sublimate-acetic mixture, etc., may give rise to fibrillar 

 structures in the cytoplasm (figs. 36, 37, 48 to 52, 110, 118). 

 These fibrillae appear in the form of striation which, at the sides 

 of the nucleus run principally in vertical direction; while, below 

 it, the horizontal course predominates. The horizontal fibrillae 

 often pass into the vertical ones so that there occurs a concentric 

 fibrillation around the nucleus. In preparations taken from the 

 alcohol-, sublimate-formalin, or bichromate-formalin material 

 containing no acetic acid, the above striation can also be seen 

 (figs. 48 to 52). 



