1895.] Microscopy. 83 
is brought into water to its point of saturation, a 40 per cent solution 
of formaldehyde is obtained, which has long been known under the 
name of formol. The use of the termination “ol,” here has been ob- 
jected to as belonging especially to alcohols, but since we have to do 
not with the vapory formaldehyde of the discoverer, but with the hy- 
drate, methylenglycol, an alcohol, this objection is not well founded. 
The first experiments as to the value of an aqueous solution of formal- 
dehyde for the purposes of disinfection, hardening and preservation, 
were made with the solution under the name of formol; therefore, the 
general custom of priority giving the honor, I shall use the term for- 
mol. 
Formol is a clear, slightly opalescent fluid with a sharp odor. By 
dilution of the fluid the odor is lessened and the liquid remains as clear 
as water.. Itis best kept in glass vessels. In metal ones it often be- 
comes of dark brown color and must then be allowed to stand quietly 
in a glass vessel before diluting for use. From the quiet liquid there 
settles a light cloudy precipitate leaving the liquid clear. A change 
of formaldehyde to an insoluable paraformaldehyde, that has here and 
there been noted, I have never met with. 
After my son, Dr. F. Blum, made the discovery that formaldehyde 
posessed besides its known antiseptic action, the noteworthy property 
of hardening animal tissues without their shrinking and without alter- 
ing their microscopic structure or staining properties, formol appeared 
to me to be the preservative fluid for which I had long sought. With- 
out loss of time, I began my experiments upon anima] and plant ob- 
jects. These gave within the short space of a few months such encour- 
aging results that I did not hesitate to publish them in a preliminary 
paper. Since then the experiments have been continued at the 
Museum der Senckenbergischen naturforchenden Gesellschaft, and in 
different places others have likewise tested the preservative properties 
of the fluid. 
Among my experiments those that follow are the most important. 
To begin with, several human embryos were placed according to age 
in formol diluted with 10 and with 20 parts of water and were finely pre- 
served. Even a foetus of 8 months in which the placenta and egg mem- 
branes were left intact, had taken up so much formol that it was hard- 
ened in spite of the resistance of the chorion to the diffusion of the liquid. 
The amniotic fluid was darkened, but the surrounding liquid remained 
clear. Somewhat finer results were obtained with smaller embryos. 
In one about 14 em. long with uninjured amnion, this being thinner, — 
3 Zoologischer Anzeiger, 1893, No. 434. 
