GLANDULAR CELLS OF THE FROG'S PANCREAS 351 



lus, as seen in figure 5. The main-nucleolus is commonly located 

 in or near the centre of the nucleus. It can never be seen applied 

 to the nuclear membrane. 



In the main-nucleolus one can notice three substances, which 

 differ in staining reactions from one another: 



Main-mass: The main-mass occupies the largest part of the 

 main-nucleolus; it is well preserved by fixatives containing no 

 acetic acid, and stained by iron-haematoxylin or Altmann's 

 acid fuchsin (figs. 1 to 8, 14 to 16, 21, 24, 63 to 65). The most 

 favorable fixatives for it are alcohol, sublimate and formalin. 

 In fact, acetic acid in the fixatives considerably diminishes the 

 affinity of the main-mass to the stains referred to, especially to 

 iron-haematoxylin. In preparations which are obtained from 

 pure sublimate material and stained by iron-haematoxylin, for 

 instance, we see that the main-mass of the nucleolus takes a gray 

 to black color, while the chromatin granules or cords are very 

 easily decolorized (figs. 1 to 6). When the same method of stain- 

 ing is applied to sections made from the sublimate-acetic mate- 

 rial, it will give an opposite result : the main-mass of the nucleo- 

 lus appears as a perfectly clear space surrounded by a deeply 

 staining shell (figs. 12, 80). It is probable that this aspect is 

 not owing to the disappearance of the main-mass by the dissolving 

 effect of acetic acid, but is to be sought in the loss of its affinity 

 for iron-haematoxylin in consequence of the changes either of 

 chemical or of physical properties produced by the above reagent ; 

 for, in sublimate preparations, the main-mass still can be made 

 manifest by staining with eosin. 



Cortical substance. This is the second constituent of the 

 main-nucleolus and surrounds it in the form of a cortex (figs. 17 

 to 20, 55, 79, 10, 11). It always stains more heavily than the 

 main-mass with most of the dyes; this is especially well marked 

 in preparations which are obtained by the Benda staining of sec- 

 tions made from Champy or Meves material (figs. 17, 18, 26). 

 The cortex is, in reality, comparable to a crust, so that the corti- 

 cal substance passes gradually into the main-mass. The contour 

 of the cortex is not smooth, but irregularly indented or with small 

 granules or short rods exhibiting the same staining reaction as 



