1897.] Microscopy. 93 
The strength of the 40 per cent. solution of formal is subject to some 
variation, since on standing for a long time it deposits a precipitate of 
metaformal and the solution is weakened by the amount of formal pre- 
cipitated. _Metaformal may also be obtained, as a bluish-white amor- 
phous powder on simple evaporation of the commercial 40 per cent. 
solution. This amorphous form is readily soluble in water heated to 
60°-70° C. It can be easily manufactured and would soon become a 
commercial article if there were a demand for it. The writer suggests 
that this would be the most convenient and economical way to use for- 
mal. Solutions of definite strength could be easily prepared, by simply 
weighing the proper amount and dissolving it in water heated to 70° 
C. Considerable expense for packing and transportation would be 
avoided. 
Action of formal on animal substances—The writer is inclined to 
believe that the action of formal varies with the kind of tissue, its 
source, whether from an aquatic or a terrestrial vertebrate, and the 
period of immersion in the liquid. 
1. Action on white of egg.—Six portions of 4 ce. each were treated 
with solutions of formal of the following strengths,—0 2 per cent.; 0.8 
per cent.; 1.6 per cent.; 3.2 per cent.; 8 per cent.; 40 per cent. The 
mixtures were put into vials and tightly corked. A flocculent preci- 
pitate resulted. It was slight in the dilute solutions, but more copious 
in the bottle which contained the 40 per cent. formal. After 48 hours, 
the dilute solutions had assumed a translucent appearance but remained 
perfectly fluid. The 40 per cent. solution was of a jelly-like consistency 
and was more opaque than the weaker solutions. 
2. The mucus of petromyzon, fishes, and necturi was coagulated ; at 
first translucent, it finally became more or less opaque and sometimes 
could be peeled off from the skin. 
The first general effect of formal on animal tissue is to coagulate the 
proteids; this fact probably accounts for its value in the Golgi method. 
Fats are apparently little altered. It has been used in this laboratory 
for the preservation of lampreys, Amia, and other fish-like vertebrates, 
of amphibia, reptiles, birds, mammals and of brains. The action on verte- 
brates up to and including amphibia has been more or less satisfactory. 
But the results upon muscles and viscera of reptiles, birds, and mam- 
mals where the specimens were immersed for four months or longer 
were far from being satisfactory. The action is rapid at first, then pro- 
ceeds more slowly, several months being required to obtain the final 
effect. However, material for immediate dissection* may be kept in 
2 per cent. formal (formal 2 ce., water 98 cc.). 
* Material will keep quite well for four to six weeks. 
