336 TRANSACTIONS OF THE [Sess. lxxxiii 



After cutting the jelly free of the edge of the Petri dish, 

 the jelly is raised up slightly on one side by slipping under 

 it the end of a broad section-lifter, and at the same time 

 this side of the dish is slowly submerged in warm water. 

 The jelly with the culture on it floats up from the bottom 

 of the dish and the gradual total submersion of the latter 

 leaves the culture free on the surface of the water. Any 

 liquefied medium present diffuses at once, and the rest of 

 the medium sinks and diffuses as it slowly melts. A 

 square of glass of suitable size, or a piece of card if the 

 specimen is to be preserved dry on a card, is passed below 

 the culture and the latter is lifted carefully from the 

 water. A certain amount of water will be taken up on 

 the support, and this serves to permit the culture to be 

 floated to any desired position. Absorbent paper applied 

 to the edge of the support takes up this excess water, and 

 the culture settles down in contact with the support and 

 adheres to it. 



If a dry preparation is wanted, all that it is necessary 

 to do now is to allow the preparation to dry slowly in 

 the air. 



Reference collections made in this way, if mounted on 

 glass supports of uniform size, may be stored in grooved 

 boxes of the kind used for the storage of photographic 

 negatives. 



If the preparation is to be much handled, the surface of 

 the culture should be protected. 1 adopt in this coiniec- 

 tion one or other of tlic following devices: — 



A watch-glass sufficiently large to cover the culture is 

 inverted over it, and is fixed in position by a tliin layer of 

 Canada balsam smeared around the edge. When this 

 first luting has set fii-m the preparation is sealed up with 

 a final luting of gold size, asphalt, or wliite cement. 

 Alternatively, the culture may be protected by a plane 

 glass disk supported on a circular wall of shellac or wax 

 spun by means of a turntable around the outside of the 

 culture. A cell of suitable depth is made and the glass 

 disk luted down with gold size, the procedure being quite 

 the same as that usually followed in mounting a nn'cro- 

 scopic object in a cell under a cover-glass. 



Cultures so prepared make very good reference specimens, 



