No. 1.] HARDENING REAGENTS. 131 
Under these conditions, the two halves of the several brains 
increase in weight in about the same way, although here again 
there are marked differences between the several encephala 
employed. It is noticeable that the hemiencephalon in the 
smaller quantity of fluid has in the three instances out of the 
four, undergone the greater increase in weight. 
This is the reaction to be expected for the following reasons : 
As we shall later see, the smaller the percentage of bichromate 
in the solution, the greater the increase in the weight of the 
specimen. As already stated, the average weight of a fresh 
hemiencephalon is 56 grms., and of this same 44.5 grms. are 
water, giving about 44 c.c. of water. 
Sooner or later this water becomes mixed with the surround- 
ing fluid, and when only 200 c.c. of a 2% solution of 
bichromate of potash are originally used, this addition of about 
22% serves to reduce the percentage of the bichromate of 
potash to 1.7%, and since the solution containing the smaller 
percentage causes the greater increase in weight, we should 
expect the specimen in the small quantities of the solution to 
become the heavier, because the dilution effected by the tissue 
fluids is more marked in these cases. 
Viewed in the light of this result, the renewal of the 
bichromate of potash solution in which the specimen is being 
hardened, should slightly retard the increase in its weight, 
because the new fluid would have a slightly larger proportion 
of the salt than that which had been diluted by the fluids of 
the specimen. 
The variation due to the change of fluid, was, in the case of 
the sheep’s brain, so slight that it was easily masked by other 
factors, and the expected influence of change was therefore not 
demonstrated. 
The renewal of the fluid also prevents the formation of 
mould. Concerning the influence of such growths on the 
change in the weight of the specimen, we have no obser- 
vations. 
Light. — Variations in the amount of light were not found 
to influence the increase of weight. We turn next to the 
influence of the temperature. Six encephala were employed, 
