598 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
end of this cylinder there is fixed a safety valve, and also a valve by 
which the pressure can be turned on. To this valve is attached a very 
thick- walled rubber hose. The method of using the filter is as follows : — 
A rubber-stoppered flask having two tubes passing through the stopper 
is the vessel used for collecting the filtrate. One tube is short and has 
its upper end enlarged and loosely packed with cotton. To the outer 
end of the long tube is attached a piece of best hose about 2 ft. long, 
divided in the middle, and having the two pieces joined by a glass 
nozzle. Further details are given concerning this apparatus, and it is 
stated that the serum prepared by it is perfectly clear, coagulates at 
exactly the same temperature as unfiltered serum, and the filtration does 
not appear to have any appreciable effect on any toxin or anti-toxin that 
may be present. The authors state that 1000 ccm. of such serum can be 
filtered in five minutes. 
(2) Preparing- Objects. 
Study of Cleavage Cells.* — It is pointed out that the principle of 
Roux’s method is very simple, but the experiments require to be carried 
out with care. That observer found that the best material for observa- 
tion was obtained from newly captured frogs at the beginning of the 
normal period of spawning. The phenomena of cytotropism are seen 
most readily between cells which are separated from the egg by cutting 
or tearing in an indifferent fluid, such as the white of a hen’s egg or a 
0*5 per cent, salt solution. For the experiments 5 to 10 ccm. of freshly 
prepared white of egg is required each day. This is prepared by 
filtering through a wad of cotton, and the preparation must be perfectly 
clear. The egg in the morula or blastula stage is first stripped of its 
gelatinous envelope and placed on a circular glass plate about 3 cm. in 
diameter. It is then covered with about five drops of the prepared 
white of egg, and torn open with two dissecting needles. The circular 
plate is next placed in a round glass dish with a rim 1 cm. high, con- 
taining 10 to 15 drops of water. The purpose of the dish with water is 
to check the evaporation of the medium in which the egg lies, and thus 
to guard as far as possible against concentration of and currents in the 
medium. These protected cells may be kept alive in a suitable medium 
for one or two days. The preparation should be immediately examined 
with a low objective. The examination of isolated cells in an uncovered 
medium has the advantage that we can easily change the position of the 
cells with needles or other means, but it is necessary to check results 
by examining preparations covered with a slip. The cover-slip for this 
purpose must be large enough for at least two of the wax feet, which 
should be 0*75 mm. high, supporting it, to fall on dry points of the 
object-plate. 
Examination of Retina of Birds. j — Prof. A. S. Dogiel used 1/10- 
1/16 per cent, solution of methylen-blue in studying the retina of 
pigeon, fowl, falcon, owl, and other birds, and was thereby able to 
demonstrate clearly the ending of the centrifugal fibres and their relation 
to the cells of the middle ganglionic layer. 
* Arch. f. Entw. Mech. d. Organismen, i. pp. 44-8. See Amer. 'Natural., xxix. 
(1895) pp. 511-12. f Arch. f. Mikr. Anat., xliv. (1895) pp. 622-48 (2 pis.). 
