NUTRIENT GELATIN. 85 



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, enam- 

 elled 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 supported on an 

 ordinary funnel; if the solution is perfect, this should 

 be very quickly accomplished. 



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, I/ (Fig. 16); the 

 end 1 is then folded over to l r , forming the fold 5; 1 

 and V are each then brought to 5, thus forming the 

 folds 3 and 7; 1 is then carried to the point 7, and the 

 fold 4 is formed, and by carrying V to 3 the fold 6 is 



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

 in this respect. 



