1889-90.] MORPHOLOGY AND PHYSIOLOGY OF THE CELL. 271 



nucleus and into the cell protoplasm, can also be determined by other 

 staining reagents, ^.^./alum cochineal, but the different stages in this phe- 

 nomena cannot be thereby so readily determined as with the other 

 method. 



I regard the yolk spherules as formed by the union of a derivative of 

 the nuclear chromatin with a constituent of the cell protoplasm. This 

 derivative of the nuclear chromatin is, possibly, the same as the haema- 

 togen which Bunge discovered in the fowl's egg united with an albumin. 

 The formation of yolk spherules in the cell protoplasm is analogous to the 

 the formation of zymogen granules in the pancreatic cells and both are 

 accompanied by changes in the nucleus and an increase in the cell 

 protoplasm. It is most natural to'conclude that the processes underlying 

 the formation both of the yolk spherules and of the zymogen granules are 

 in a general way alike. We see many facts supporting this view. In the 

 developing ovum there are phases in the elaboration of the chromatin and 

 the formation of nucleoli (plasmosomata) comparable to the production of 

 chromatin in the nucleus of the resting pancreatic cell, and to the appar- 

 ent conversion of this chromatin into safranophilous substance which 

 diffuses through the nucleus in the exhausted cell. We see a further 

 parallel to the formation of yoke spherules in that as the nucleus loses its 

 safranophilous substance the cell protoplasm acquires safranophilous 

 granules. If we accept the parallel so far as correct, we may then 

 assume that the chromatin of the nucleus of the pancreatic cell gives 

 rise to a substance which we may call " prozymogen," sometimes dis- 

 solved in the nuclear substance, sometimes collected in masses (plasmo- 

 somata), and finally diffused into the cell protoplasm, uniting with a 

 constituent of the latter as zymogen. This is, I think, the true explana- 

 tion of the phenomena of secretion. 



With the help of this theory we can explain why it is that in certain 

 pancreatic cells the protoplasmic masses contain, as described above, eosin- 

 ophilous granules of exactly the same size as those of zymogen, but 

 unlike the latter in that they are not dissolved out by solutions contain- 

 ing acetic acid. The protoplasmic masses swallowed by a pancreatic cell, 

 cannot be of the same composition as the cell protoplasm, and are not 

 amenable to the laws which govern the nutrition of the cell as a whole. 

 When the prozymogen diffuses from the nucleus to the cell it invades 

 the protoplasmic masses enclosed, and it becomes united with a constitu- 

 ent of the latter, thereby forming a compound similar to zymogen in 

 some respects : the capacity for forming spherules, the eosinophilous and 

 safranophilous reaction, but differing from it, as already said, by being 

 insoluble in solutions of acetic acid. 



