Journal of Applied Microscopy. 549 



An Apparatus and Method for Preparing Agar. 



In the April, 1898, number of this Journal, Miss Marion H. Carter, of 

 Cornell University, published a method for preparing agar for the cultivation of 

 bacteria. Being impressed with its simplicity, I determined to give it a trial, 

 inasmuch as it promised to save considerable labor. Repeated trials have 

 proved that much of the drudgery connected with the preparation of this impor- 

 tant medium may be avoided by employing Miss Carter's method. 



The object of the present article is to emphasize this fact, and to describe 

 an apparatus which I have devised for employing the method. 



The apparatus consists mainly of an ordinary nine-inch copper funnel, with 

 an inch-wide perpendicular wall around the top, which may be obtained 

 ready-made at the shops. To it are added a cover, and three legs having a 

 spread equal to the greatest diameter of the funnel. The spout may be closed 

 by means of a rubber stopper, or a cap may be soldered on. In the former 

 case, the funnel will be found useful in other directions. A funnel of this size 

 will hold a gallon, and gives ample room for work. 



If one liter of medium is wanted, place about 900cc. of bouillon in the funnel, 

 add ten or fifteen grams, of pulverized agar, according as a 1 per cent, or a 1^^ 

 per cent, solution is desired, to the other lOOcc, and mix thoroughly by rubbing 

 up in a mortar or a beaker. Place the mixture thus made in the funnel and 

 stir thoroughly. If the agar is in the stalk form, it may be put directly into 

 the funnel after having been cut up. Now place the funnel with its contents 

 in a 11 X 13-inch can, containing sufficient water to last for two hours, and boil. An 

 Arnold sterilizer may be used instead of the can, if desired. After boiling for 

 an hour, turn off the gas, remove the covers, and stir the agar solution, espec- 

 ially that in the spout of the funnel. Replace the covers, and boil another hour. 

 Turn off the gas, and allow the whole to cool, taking care not to disturb the 

 solution at this time. After solidification has taken place, remove the funnel, 

 invert it on a glass plate, and the agar will come away as a mould. That portion 

 from the spout will be found made up of the insoluble materials which ordinarily 

 interfere with filtration, and which usually amount to about 1 per cent, of 

 the whole mass. It is to be sliced off and thrown away. The remaining portion 

 will be sufficiently clear for ordinary purposes, and may at once be remelted, 

 distributed, and sterilized. Should it not be sufficiently clear, it may be clarified 

 by the usual method. Filtration may then be readily accomplished, since most 

 of the foreign and insoluble matter has been removed by the sedimentation 

 process. 



As might be supposed, the nutritive qualities of agar thus made are in no 

 way interfered with. Over fifty different species of bacteria have been grown 

 upon it with perfect success, by the writer. 



Charles F. Dawson, M. D. 

 Washington, D. C. 



