526 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
requisites of a satisfactory solid medium it is quite deficient. The 
objections to the method with reference both to the process itself aud 
the character of the resultant agar are three in number. (1) The 
difficulties attending the filtration of the agar. This process alone often 
requires a very considerable length of time besides the use of a hot 
filtering apparatus that must be provided especially for this purpose. 
(2) The presence in the sterile agar of a flocculent precipitate that is 
invariably thrown down during the process of its sterilization, and which 
greatly interferes with its usefulness, especially in making roll and 
plate cultures. (3) The variation in the consistency of the agar. It is 
impossible to obtain this material of the same consistency, as the agar is 
only partially dissolved, even after long boiling, in the simple beef- 
infusion. The coagulation of the albumen ensheaths the stems of agar, 
floats them to the surface where they remain imbedded in the firm, 
albuminous coagulum. This property of the agar is worthy of con- 
sideration, for with the varying consistency of the medium a consequent 
change follows in the character of the growth of most germs. 
For the purpose of securing a process for the preparation of nutritive 
agar that was free from the above mentioned difficulties I have reviewed 
carefully the method of Jacobi,* Yon Freudenreich,! and Cheesman,J in 
all of which I found difficulties that were equally as objectionable as 
those possessed by the original method. 
The use of a solution of beef-extract in distilled water, instead of the 
simple beef-infusion made directly from the fresh meat, was also tried, 
but the agar thus prepared did not favour as vigorous a growth of many 
germs as when prepared from the fresh meat-infusion. So feeble was 
the growth of many germs upon this agar that the method was aban- 
doned, although very satisfactory in other respects. 
In the course of this experimental work it was found that when the 
stems of agar were cut into small pieces and boiled in a fluid containing 
no coagulate material, that it was entirely broken up and the soluble 
portion dissolved. The insoluble particles that remained suspended in 
the liquid were easily and completely removed by the addition of egg 
albumen, and subsequent boiling and filtering. From these facts a 
method for the preparation of nutritive agar was derived, which consists 
in first preparing the neutralized beef-infusion-peptone, and thus getting 
rid of all coagulable material before the agar is added. This process is 
effective in greatly diminishing the time and attention required for the 
preparation of this medium. The medium can always be made of the 
same consistency, as all of the agar that is added is dissolved. It 
remains free from precipitates when sterilized, and its nutritive qualities 
are as favourable to bacterial growth as when it is prepared after the 
original method. 
(1) The preparation of the beef -infusion-peptone . — The method of 
preparing this liquid is practically the same as that already in use in 
most laboratories. Finely chopped or ground beef (freed from fat) is 
macerated in distilled water for from 12 to 18 hours in a cool place. 
The distilled water is added in the proportion of 200 ccm. to each 
* Centralbl. f. Bacteriol. u. Parasitenk., iii. (1888) p. 538. t T. c., p. 797. 
X American Naturalist, xxii. (1888) p. 472. 
