Journal of Applied Microscopy. 301 



A Method for Making the Three Principal Artificial Media, 



Based on the Bacteriological Committee's 



Recommendations. 



It is scarcely necessary, at this date, to recapitulate the reasons for the use 

 of simple, and particularly of exact, methods in the preparation of culture 

 media. 



The first important impulse in this direction was given by the Convention 

 of Bacteriologists, summoned by the Committee on Water Supplies of the 

 American Public Health Association in 18!)5. This convention, the proceedings 

 of which were published in the October number of the Journal of that Association, 

 appointed a Bacteriological Committee, including a number of the best known 

 bacteriologists in America, empowered to draw up a series of methods selected 

 from the best extant at the time which should be recommended as standards, 

 particularly for species differentiation. 



The writer, having been associated with a member of the committee who 

 dealt particularly with the question of the preparation of nutrient broth, gelatin, 

 and agar-agar, was able to suggest certain minor changes in the tentative 

 methods published in 1895, which were incorporated in the recommendations of 

 the Bacteriological Committee, published finally in the Journal of the American 

 Public Health Association, January, 1898. 



Further work on the subject has led the writer to suggest here a slight 

 change in the preparation of nutrient broth, designed to prevent the precipita- 

 tion of albumens during sterilization which may occur if the methods of the 

 Bacteriological Committee are rigidly followed. The tabulation of the neces. 

 sary steps, given below, will demonstrate this point clearly. Step No. 14, 

 in this table, is recommended by the Bacteriological Committee to follow Step 

 No. 10. The writer has placed it in its present position for the reason already 

 given. 



In June, 1898, Ravenel published in The Journal of Applied Microscopy 

 an excellent method for the preparation of nutrient agar, certainly the best which 

 has yet appeared. The writer, working independently along similar lines since 

 1895, arrived at a quite similar method, which has an advantage over that of 

 Ravenel, however, in that it does not require the use of the autoclave. In the 

 table, this method has been so developed as to place the preparation of the three 

 principal media on an analogous basis, at the same time adhering closely to 

 the methods and spirit of the Bacteriological Committee's recommendations. 

 (See table.) 



A question naturally arises as to whether or no the extraction of meat with 

 an equal quantity of water, as here recommended for nutrient agar, will yield 

 the same results as the extraction of the same quantity of meat with twice its 

 weight of water, the method usually employed. The writer has found that the 

 former process yields a slightly smaller amount of total solids. The estimation 

 was made for the writer by Dr. Charles Harrington, of the Laboratory of 



