and Laboratory Methods. 



■l-lQi 



Laboratory Notes. 

 L 



A Simple and Effectual Method for Keeping Media and Cultures Sealed. — Repeated 

 efforts to devise some means of keeping media and cultures hermetically sealed 

 resulted in the following device : Paraffin stoppers are made from paraffin of 

 the highest melting point (71 °C.). These are kept in a solution, containing 50 

 per cent, of alcohol and 3 per cent, of copper sulphate, until used. The stop- 

 pers are of various sizes to fit the various sized test-tubes {¥\g. \-c). To seal 

 the tube a size somewhat larger than the 

 tube is selected, the cotton plug is thor- 

 oughly singed and inserted to within ^ 2 -inch 

 from the end. The latter is warmed and 

 the stopper inserted. The tube then has 

 the appearance of Fig. 1-b. When required 

 for inoculation, the end of the tube is 

 gently warmed and the stopper removed. 

 It may then be held between the fingers 

 during inoculation and replaced, or it may 

 be rejected and placed back into the solu- 

 tion, and the cotton plug alone used. The 

 advantage of this method over rubber caps 

 is, first, in the cheapness and, second, 

 freedom from molds, as the small amount 

 of copper sulphate-alcohol adhering to the 

 stopper is sufficient to kill the molds on the 

 upper end of the cotton plug. The ad- 

 vantage over a paraffined plug is that it is 

 less greasy and leaves the cotton plug dry 

 and expansile. Solid media in tubes with 

 paraffined plugs cannot be melted without 



the paraffin running down into the medium and spoiling it for plate cultures. 

 This is entirely avoided by the use of the stopper. 



To make the paraffin stoppers, the following method is employed : A strip 

 of ordinary stiff writing paper is rolled into a tube and inserted into a test-tube 

 (Fig. \-a). By rotating the paper tube, it is so adjusted as to fit the test-tube 

 snugly. Melted paraffin is then poured into the paper tube and the whole at 

 once placed in running cold water. When solidified the walls of the test-tube 

 are slightly warmed and the inner paper mould removed by a slight rotatory 

 movement. The paper is then easily peeled off from the solid paraffin stick. 

 This is cut up into cylinders of desired lengths and the latter trimmed into shape 

 with a warm knife. The whole procedure takes but a few minutes. 



IL 

 The Preparation of Loeffler's Blood Serum Plates for Diphtheria Bacilli. — In the 



preparation of Loeffler's blood serum we found the method first proposed by Miss 



Fig. 1. — {a) Paper mould in test-lube; 

 (/') agar-agar slant with plug and paraf- 

 fin stopper; (c) paraffin stopper. 



