Section IV., 1908. [Ill] Trans. R. S. C. 



y. — A method for Preparing Gelatine Plates for Museum or Class 



Purposes. 



By F. C. Harrison, Bacteriological Laboratories, Macdonald College, 



P.Q., Canada. 



(Read May 26, 1908.) 



It is often necessary to prepare gelatine plates for class purposes, 

 and whilst the preparations of giant colonies as prepared by Krai are 

 very useful yet the}^ do not present the features often desired in a 

 preparation. 



The method consists in preparing gelatine plates in the ordinary 

 manner, but, as a rule, four or five dilutions are made from the first 

 tube of melted gelatine. After the tubes are inoculated and well 

 shaken by rolling between the palms of the hands, the contents are 

 poured on to sterilized plates of glass 3i" x 4^" old photographic 

 plates which have been carefully cleaned being generally used. The 

 plates are very carefully levelled, and as soon as the gelatine has set, 

 they are placed in proper double dishes and set in the cool incubator 

 until the colonies develop. When the colonies have attained their 

 most typical appearance, the plates are placed in a dish containing 

 a solution of 5 to 10% of formalin, and allowed to remain in this 

 liquid for one to three hours, depending on the thickness of the gela- 

 tine. They are then taken out and the edges trimmed with a knife, 

 leaving a slab of gelatine about 3" x 3" square in the middle. They 

 are then immersed again in the formalin bath and a clean sterilized 

 glass plate of the same size is gently placed on the top of the gelatine 

 so as to exclude all air bubbles. The gelatine plate and its cover 

 are then taken out, allowed to drain for a moment, and then the four 

 edges are successively dipped into melted paraffine kept in a tray 

 about 5" long. As soon as the paraffine has solidified, the edges are 

 carefully inspected and if any holes are noticed they are filled in with 

 melted paraffin poured from a small spoon. Thus a glass cell is 

 formed with paraffine sides. After cleaning off the surplus paraffine 

 on the glass, the sides are bound with linen or paper binding strips, 

 the same as used for lantern slides, and known as passe partout bind- 

 ing. The name of the organism and other information is written 

 on the binding strip in white ink and the slides stored in the same 

 manner as ordinary diapositives. 



Most bacterial colonies give good preparations this way; even 

 liquefying bacteria, if the colonies are not too old, give good prépara- 



