224 A. B. MACALLUM. 
as definitely upon this as upon the relations, in this respect, 
observed in the pancreatic cells of Amblystoma, for | have 
not been successful in my efforts to obtain, from examples of 
the latter animal, preparations of the gastric glands illustrating 
marked variations in the stages of secretory activity, and have 
had to rely upon those made from the cat and dog, in which 
the chief cells are comparatively small and less favorable for 
observation on this point. 
It is only in the mucous glands of the skin of Amphibia, and 
in the renal tubules of Vertebrates generally, that I find 
exceptions to the rule that glandular secretion is associated 
with the presence of an iron-holding cytoplasm. I have not 
found any exceptions in Invertebrates to this generalisation, 
but my observations have not been comprehensive enough on 
this point, and I must speak with some reserve in regard to it. 
In the Protozoa, as I will show further on, the presence of 
assimilated iron in the cytoplasm seems to be a constant 
feature, the iron not being confined to any part of the cell, but 
uniformly distributed through it, and there is a probability 
that this cytoplasmic iron-holding compound is also associated 
with the secretion of ferments functioning in the digestion of 
the ingested food. In the glands named above, which are 
mentioned as exceptional instances, the absence of assimilated 
iron from the cytoplasm may be explained on the ground that 
the secretory process of a renal cell is widely different from 
that of a pancreatic cell, the cytoplasm in the latter, but not 
in the former, elaborating a portion of its own constituents to 
furnish the secretion, whereas in the renal cell the process is 
largely one of transference only. Ifthe explanation should hold 
in all possible cases of exception, then it would follow that the 
iron-holding compound is an important element in the elabora- 
tion of the zymogens. I have elsewhere! pointed out the rela- 
tions that obtain between the chromatin of the nucleus and of 
the cytoplasm of the pancreatic cell, on the one hand, and the 
formative process resulting in the production of zymogen on 
1 “Contributions to the Morphology and Physiology of the Cell,” ‘Trans, 
Canadian Institute,’ vol. i, part 2, p. 247, 1891. 
