ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 533 



The carrier can easily be constructed with a broad flange to facilitate 

 this, and in the event of breakage few would experience any difficulty in 

 fixing another cover. In addition to the cemented cover-glass, it is 

 only necessary that the carrier should accurately fit into the box in such 

 a way that an elastic band may be placed round the rim over the line 

 juncture, thus rendering the appliance practically airtight (fig. 122). 



Fig. 12'2. , 



Method for Freeing Paraffin from Cedar-wood Oil.* — In the use 

 of cedar-wood oil for imbedding tissues in paraffin it is a disadvantage 

 that the oil is not volatile, and is thus retained in the paraffin, rendering 

 it unfit for further use. W. Mair has found that by the following 

 simple method a large part of the paraffin can be recovered in a tolerably 

 pure condition. The contaminated paraffin is allowed to solidify at room 

 temperature. It is then placed on top of a pledget of cotton-wool in a 

 suitable vessel and allowed to remain in the incubator at body-tempera- 

 ture over-night. Next morning the wool will be found saturated with a 

 melted mixture containing a great deal of oil and little paraffin, while 

 the solid mass of paraffin above is fairly pure. This is removed and 

 placed in the paraffin oven to filter, and the filtrate will be found quite 

 satisfactory for at least the first paraffin bath. 



Method for Preserving Bacterial Cultures for Class Purposes.f 

 E. S. (x. Fowler writes : After subcultivating the purer colonies on 

 fresh tubes and obtaining results which show the main features of par- 

 ticular growths, I pour on to the sloped or straight surface (streak and 

 stab cultures) of the medium a covering some \ in. to f in. deep of the 

 following preparation : Gelatin, 50 grm. ; formalin (40 p.c.) 20 minims ; 

 water (distilled), 1 fl. oz. The gelatin is dissolved in the water by heat, 

 and when nearly cool the formalin is gently stirred in, so as to avoid 

 air-bubble formation. Just before it sets it is poured over the growth 

 to the depth required, and the plugs replaced and the tube left in posi- 

 tion to cool. I next cut the wool plugs level with the tube mouth, and 

 dip the plugged end into melting white wax and so seal them. The 

 specimen is stored preferably in a cool, dark place. The preparation, 

 being transparent, seems to serve the following purposes: (1) If the 

 growth is not quite pure no further growth takes place after treatment, 

 so that the specimen is fixed with features required ; (2) no growth 

 occurs from contamination, with ordinary care ; (3) being transparent, it 

 does not interfere with good viewing of the growth ; (4) it checks 



* Brit. Med. Journ. (1905) i. p. 1381. t Tom. oil, p. 1412. 



