ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
889 
enzyme allied to trypsin, both of which are found in milk after the action 
of certain kinds of bacteria, in general those having a liquefying action 
on gelatin. Sterilized milk is inoculated with the bacterium, which is 
allowed to grow for 7-10 days after coagulation has occurred. The 
milk is then carefully shaken up with distilled water, and next passed 
through a porcelain filter. The clean filtrate contains all the soluble 
ferments. It is frequently colourless, but is often of an amber hue, or 
even brownish. From this material the soluble ferments may be preci- 
pitated by alcohol, collected and dried, the dried precipitate having the 
property of coagulating milk and peptonizing gelatin. The rennet is 
separated from the pepsin by acidulating the filtrate with 0 * 1 per cent, 
of sulphuric acid, and then adding common salt in excess. When the 
fluid becomes saturated with salt a snowy scum forms on the surface. 
This is nearly pure rennet ferment. The scum is then removed and 
dried. The snow-white powder is rennet mixed with salt, and possibly 
some other impurities. 
The rennet ferment seems to be more quickly developed at moderately 
low (20°) temperatures than at higher ones (35°), which are more favour- 
able to the pepsin ferment. 
(2) Preparing- Objects. 
Investigation of Origin of Vascular Germs in the Chick.* — M. L. 
Vialleton opened the eggs in water to which a small quantity of salt 
solution had been added, and which had been heated to 35° ; the blasto- 
derm was rapidly cut out and placed on a glass plate ; it was then treated 
with a 1 per cent, solution of silver nitrate, washed with distilled water, 
and put (in darkness) in 70 per cent, alcohol for from six to twelve hours. 
On being removed from the alcohol it was put in an alcoholic solution 
of borax-carmine, in which it remained till it was sufficiently stained ; 
it was then washed with 70 per cent, alcohol slightly acidulated with 
hydrochloric acid, dehydrated completely in 90 per cent, and absolute 
alcohol, and mounted in dammar. Owing to the reduction of the nitrate 
of silver, the boundaries of the epithelial cells were well marked, while 
the borax-carmine stained the nuclei in such a way that a fine preparation 
was obtained, in which a number of interesting histological details could 
be made out. The only fault of this method of preparation is that the 
reduction of the nitrate of silver sometimes goes too far, and sometimes 
the ectoderm becomes folded. 
Spermatogenesis of Gryllotalpa.| — Dr. O. vom Eatli obtained best 
results with Flemming’s chrom-osmo-acetic acid, “ Hermann’s fluid,” 
and a mixture of picr-osmo-acetic acids. As stains, the most successful 
were alum-cochenil (21 hours in warm temperature), and safranin-gentian- 
orange. 
Examination of Gills of Palsemonetes varians.J — Mr. E. J. Allen 
found that the gills of this Crustacean were somewhat difficult to preserve ; 
the use of sublimate and alcohol failed to give satisfactory results. 
With strong Flemming’s solution he was able to obtain preparations 
* Anat. Anzeig., vii (1892) pp. 624 and 5. 
f Arch. f. Mikr. Anat., xl. (1892) pp. 102-32 (1 pi.). 
X Quart. Journ. Micr. Sci., xxxiv. (1892) pp. 75 and 6. 
3 o 
1892. 
