472 General Notes. 
PHYSIOLOGY .! 
NOTES ON THE PREPARATION OF NUTRIENT GELATINE AND 
AGaAr.—The practical worker in Bacteriology deplores the loss of time 
usually attendant upon the preparation, and especially upon the 
filtration of nutrient gelatine and agar. The method formulated 
by Koch and closely followed by most workers, is very satisfactory 
in producing good, clear culture media, but a few modifications 
render the procedure a much less formidable one, and as the changes 
to be suggested are simply those of detail, it may be well to state in 
brief the method now in use in this laboratory, which after consid- 
erable trial gives uniform and satisfactory results. 
One pound (4 kg.) of finely chopped beef, as free as possible 
from fat and gristle, is mixed with 1000 c. c. of distilled water and 
kept in a cool place for 12 or 18 hours. It is then strained, cold, 
through a coarse cloth, into a wide-mouthed “agate ware” or 
“enameled iron” vessel of sufficient size, and 5 gm. of C. P. so- 
dium chloride, 10 gm. of pepton,! and 100 gm. of gelatine’ 
(or 10 gm. of Agar) are added. This is then placed in a water 
bath’ (to which a large handful of rock salt has been added, if 
agar is to be prepared) and the gelatine (or agar) melted as rapidly 
as possible. The fluid is then neutralized by the careful addition 
of sodium bicarbonate in solution, and the boiling continued for a 
few minutes after, in order to precipitate the phosphates. 
The fluid is now cooled by running water, to such a temperature 
as will not coagulate the white of egg, yet not enough to solidify it, 
when the whites of two eggs, thoroughly beaten up are mixed with 
it, and the whole boiled for half an hour. 
Filtration which has usually been effected by means of filter pa- 
per, can be much more rapidly performed by the use of absorbent cot- 
ton in large quantity. The pores of the paper become clogged by the 
fine precipitates and by the cooling of the medium, and even with 
the use of the “hot funnel ” the filtration is sometimes very slow. 
Cotton, on the other hand, presents in its meshes a much larger 
surface for the entanglement of the fine precipitates, and when used 
in large quantity, allows the gelatine (or agar) even when not very 
hot, to flow through it rapidly. The preparation of the filter is as 
follows: The absorbent cotton is unrolled, and sterilized in bulk in 
the hot-air chamber, care being taken not to char it. A six-inch 
1 This department is edited by Prof. Wm. T. Sedgwick, of the Mass. 
Institute of Technology, Boston, to whom brief communications, books 
or review, etc., shou e sent, 
2 Comte fils Gelatine premiere qualite, gives excellent results. it 
3 Pepton Sice. Extru, from G. A. Hesterberg, Berlin, is used, aS 
imparts no color. 
‘The form that has been found most convenient is known as AN 
agate ware ‘‘ Milk or Rice boiler.” 
