386 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
following method : — To a solution of equal parts of 2 per cent, formalin 
and Perenyi’s fluid was added enough common salt to increase the density 
of the mixture to that of sea-water, that is, until a Ctenophore placed 
in it barely floated. This adjustment of the density of the surrounding- 
medium prevented the Ctenophores collapsing of their own weight. After 
remaining for about half an hour in this fluid they were transferred to 
4 per cent, formalin. The density of each had been increased by the 
addition either of Epsom salts or common salt. The former is probably 
better than the latter for increasing the density of the fluid. 
Preserving Brains.* — Dr. A. Lanzillotti-Buonsanti advocates the 
use of formalin for preserving brains. This fluid contains 40 per cent, 
of formic aldehyde, and may be mixed with water in various proportions. 
The author left dogs’ brains for 10-12 days in a 2 per cent, solution, 
and then placed them for a like period in glycerin. The results were 
better than with Giacomini’s method. 
Wiese’s Preserving Fluid.t — Dr. A. B. Meyer publishes a letter from 
Wiese to the effect that his fluid is disappointing only because collectors 
use it carelessly and not enough. Each object must have 3-4 times its 
own volume of preserving fluid. But the letter does not make clear 
whether even a large quantity of the fluid will prevent soft specimens, such 
as fishes, from falling to pieces, which was what Meyer complained of. 
(6) Miscellaneous. 
Standard Unit of Size for Micro-organisms. { — Mr. G. C. Whipple, 
after pointing out that the results of the microscopical examinations of 
water by the ordinary methods are often misleading owing to the custom 
of recording the number of organisms present in a cubic centimetre of 
water examined, without regard to their character or size, shows that it 
is advisable to use some unit by which the actual quantity of animal and 
plant matter present may be expressed ; such a standard would be a 
square 20 microns wide, having an area of 400 square microns. This 
is suggested because it has already been used in estimating amorphous 
matter, because it is about the size of several common organisms, and 
because it is a unit whose size can be easily carried in the mind. 
It will be found of great advantage to have the ocular micrometer 
divided as follows : the square, which should cover one square millimetre 
on the stage of the Microscope, is first divided into four equal squares, 
and each of these quarters subdivided into smaller squares, each of which 
is equivalent to twenty-five standard units. 
Two plates are given showing how there is a general parallelism 
between the profile (curve) of the albuminoid ammonia and that of the 
organisms expressed in terms of the standard unit, while the curve of 
the actual numbers of the organisms does not accord well with the 
chemical analyses. 
It should be noted that this volumetric method has been used for 
over two years at the Boston Waterworks, and several other biological 
laboratories have since adopted it. 
* Mon. Zool. Ital., v. (1894) pp. 273-5. 
t Zool. Anzeig., xviii. (1895) pp. 122-5. 
■% Amer. Mon. Micr. Journ., xv. (1894) pp. 377-81 (2 pis.). 
