686 Proceedings of Royal Society of Edinburgh. [sess. 
with those who maintain that chromatin elaborated elsewhere is 
stored up in the nucleolus [Sabotta (23), Labbe (12), Mingazzini 
(18), etc.]. I therefore agree with Pizon (21), and those other 
observers who hold that the nucleolus is entirely, or at least in 
great part, composed of effete material. 
The changes occurring in the nucleo-hyaloplasm are also interest- 
ing. When precipitated with mercuric chloride, during the resting 
condition, the precipitate lanthanin of M. Heidenhain (7) stains 
pale blue. As activity proceeds, these granules become more and 
more scanty, hut just after the nucleus reaches its maximum of 
shrinkage, the lanthanin becomes very abundant, and stains of a 
deep blue colour, which gradually gives place to a beautiful lilac 
tint as repair goes on, finally returning to pale blue when repair is 
complete. This denotes that the nuclear juice undergoes chemical 
change during nuclear activity. Strasburger (26) in 1892 stated 
that the reaction of nuclei depended upon their condition of 
nutrition ; well nourished nuclei being erythrophile, and poorly 
nourished ones cyanophile. This corresponds well with what has 
just been stated. 
The great fatigue exhibited by the nuclei of secreting cells 
during the conversion of zymogen into zymin by the action of very 
dilute acids has for a long time been a puzzle to me, for one would 
suppose the manufacture of zymogen would he far more exhausting 
than its mere passage out of the cell into the gland lumen. 
The researches of MacCallum (14) of Toronto throw light upon this 
subject. He maintains that zymogen is preceded by a substance rich 
in phosphorus and iron produced at the expense of the chromatin of 
the nucleus. This substance he terms prozymogen, which becomes 
united with a constituent of the cell protoplasm to form zymogen. 
Mouret (19) also takes a similar view of the production of zymogen, 
and he named the antecedent substance “ prezymogen,” and 
Bensley (3) has corroborated these researches in his recent paper 
on the stomach. 
I believe that the nuclear exhaustion so evident in my speci- 
mens is indeed brought about by the manufacture of prozymogen. 
Almost directly after the cell had begun to pour out its secre- 
tion, the nucleus commences to form a new supply of prozy- 
mogen at the expense of its store of chromatin, and that the 
