NUTRIENT GELATIN. 



77 



bath, in the steam sterilizer, or over a free flame. If 

 the latter method is practised, care must be taken that 

 the mixture is constantly stirred to prevent burning at 

 the bottom and consequent breaking of the flask, if a 

 flask is employed. 



For some time it has been our practice to use, for the 

 purpose of making both gelatin and agar-agar, enamelled 

 iron saucepans instead of glass flasks ; by this means 

 the free flame may be employed without danger of 

 breaking the vessel, and, with a little care, without fear 

 of burning the media. Under any conditions it is 

 better to protect the bottom of the vessel from the 

 direct action of the flame by the interposition of several 

 layers of wire gauze, a thin sheet of asbestos-board, or 

 an ordinary cast-iron stove-plate. 



When the gelatin is completely melted, it may be 

 filtered through a folded paper filter on an ordinary 

 funnel ; if the solution is perfect, this should be very 

 quickly accomplished. 



Fig. 1». 



For the filtration of such substances as gelatin and 

 agar-agar it is of much importance to have a properly 

 folded filter. To fold a filter correctly, proceed as fol- 

 lows : A circular piece of filter paper is folded exactly 

 through its centre, forming the fold 1, 1 (Fig. 13) ; the 



