1895.] Microscopy. 87 
The use of a very dilute solution of formol works badly for the reason 
that from such a fluid the water is absorbed very decidedly. At least 
fruits became swollen more often than plants in the dilute solutions. 
Cherries, for instance, keep well in a 1:30 solution, but in one of 1:60 
or 1:80 they burst open. The entrance of the fluid into the colored 
envelopes of flowers is also very noticeable. How dilute the solution 
may be for the different plants is difficult to say. It must be deter- 
mined by experiment. 
Of Cryptogamous plants I have till now experimented only with 
truffles (1:10) and young Phallus impudicus (1:30). This last was cut 
in two and forms an excellent preparation. 
Cohn declares that formaldehyde forms an excellent means of pre- 
serving Leuconostoc and chromogenous bacteria since the jelly and 
color are not changed.° 
The value of the fluid for preserving bacteria has been noticed by 
Hauser.’ He shows that gelatin in which micro-organisms are grown 
is changed by formaldehyde vapor so that it will not become fluid, and 
that gelatin already peptonized becomes hard again in the vapor. 
Neither the gelatin nor the micro-organisms suffer a noticeable change, 
and the preparations can be kept for demonstration or museum pur- 
poses. 
In microscopic sections of plants that have been in the preserva- 
tive (1:20) for several months the cell wall, protoplasm and chlorophyll 
bodies appear as in fresh specimens. 
I have not yet undertaken to determine the freezing point of the 
formol solution, but will remark that during the past cold winter in 
an unheated store room the diluted solution was not frozen, and that 
even in the open air at a temperature of—18° C the concentrated solu- 
tion remained fluid. 
In conclusion the properties of formol as a preservative medium may 
be summed up as follows: 
Animal objects are hardened with shrinking, and without losing 
their microscopic structure or staining properties. 
The natural form and color is preserved. 
The eye remains much clearer than in alcohol. 
The mucous of slime producing animals is not coagulated and re- 
mains transparent. 
The coloring matter of blood in tissues apparently disappears, but 
may be quickly restored by a high per cent alcohol. 
6 Bot. Centralbl., Vol. lvii, No. 1, 1894 
7 Münchener med, Wochenschrift, 1893, Nos, 30 & 35. 
