NUTRIENT GELATIN. 



81 



which all acid has been carefully washed. 1 The gelatin 

 is added in the proportion of 10 to 12 per cent. Its 

 complete solution may be accomplished either over the 

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

 If the latter method be practised, care must be taken 

 that the mixture is constantly stirred to prevent burn- 

 ing 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 burn- 

 ing 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. 



FIG. 13. 



When the gelatin is completely melted, it may be fil- 

 tered through a folded paper filter on an ordinary fun- 

 nel ; if the solution is perfect, this should be very quickly 

 accomplished. 



1 Hesteberg's acid free, gold label gelatin has given us entire satisfaction 

 in this respect. 



