STUDIES ON THE PANCREAS OF THE GUINEA PIG 365 



with the best apochromatic objectives. In preparations stained 

 intra vitam with neutral red or with janus green the cells of the 

 islet are intensely stained and when such a preparation is studied 

 under an apochromatic immersion lens it is seen that the stain 

 is contained exclusively in the small granules described above, 

 which are imbedded in a colorless and apparently structureless 

 protoplasm. When such preparations are exposed to the air, 

 however, in the cells stained with janus green the mitochondrial 

 granules also take up the stain though they are difficult to ob- 

 serve among the specific granulations of the cell. 



Both in the fresh preparation and in those stained in neutral 

 red the small granules exhibit brownian movement. 



If fresh preparations of the islet cells stained with neutral red 

 are kept under observation for one-half to one hour in isotonic 

 salt solution, a change in the structure of the cell may be observed, 

 the protoplasm then becomes coarsely vacuolated, or alveolar in 

 structure, the granules disposing themselves in the partitions be- 

 tween the alveolae. 



In studying fresh preparations of the islet cell the method of 

 obtaining sections by freezing must be avoided, for the granules 

 disintegrate when frozen and in the neutral red preparations 

 the dye is dispersed throughout the protoplasm. 



An interesting feature of the preparations stained by neutral 

 red intra vitam is that owing to the small size of the granules it 

 is possible to observe in the still living cell the outline of the canals 

 of Holmgren, which appear as colorless spaces among the deeply 

 stained granules. 



The examination of these preparations also dispels the idea that 

 the cells of the islet constitute a syncytium, for not only can the 

 outlines of the individual cells be seen perfectly in the intact islet, 

 but a slight pressure on the cover glass suffices to separate the cells 

 from one another. It is thus possible, without teasing, easily 

 to obtain large numbers of single islet cells for high power study. 



In the single cells isolated by the methods just described the 

 granules show frequently an unequal distribution in different parts 

 of the cell. For example, many cells of elongated shape show 

 the granules concentrated in each end of the cell while the inter- 



