552 SUMMARY UK CURRENT RESEARCHES RELATING TO 



spirit may evaporate inwards and be condensed in the fluid mountant, 

 and many slides may be spoiled by a milky fog caused by the con- 

 densed denaturant, which is not transparent when mixed with water 

 any more than methylated spirit is. The quantity required is not large, 

 so absolute alcohol is not prohibitive. 



Use the mountant as thickly as it can be worked to flow, and make a 

 heavy ring on the slide. Of course, it is preferable to do a fair quantity 

 at one time. This sets in about 15 minutes, and dries reasonably hard 

 in a day. This ensures perfect contact of the cement to glass slip. To 

 cement the rings, take a scraping of soap from the piece in use, and 

 spread it on the turntable centre. A ring, flatted on coarse emery 

 cloth if metal, or coarse sandpaper if vulcanite, can be pressed on to 

 the soap and adjusted centrally with sufficient firmness to be cemented 

 all round, leaving a more level ring than can be otherwise obtained. 

 The next day, or later, a thin ring of cement can be put on the slip 

 and the ring adjusted in place. When hardened, there will be perfect 

 contact of cement and glass, with perfect contact of cement and ring, 

 with an elastic layer of cement in between, which is capable of absorb- 

 ing any small variation under the exercise of pressure. A ring fixed in 

 this manner is likely to remain permanent if the further mounting 

 operations are properly performed. 



Direct Enumeration of Bacteria in Water.* — In the bacterio- 

 logical examination of water samples, Y. Amann counts the number of 

 micro-organisms by direct observation of a known volume of the water 

 with dark-ground illumination. For this procedure are required the 

 ordinary accessories for oblique illumination, and a ruled slide of the 

 type used for the enumeration of blood-cells. The author finds that 

 by this method much higher figures are obtained than with methods of 

 plate cultivation. For example, a sample of water which, when plated, 

 gave growth of 584 organisms, was found, by the method of direct 

 enumeration, to contain 86,000 organisms per cubic centimetre. This 

 method permits of the enumeration of organisms which are incapable of 

 growth upon ordinary media, and of the differential counting of motile 

 and non-motile bacteria. 



Method of Preserving Brain Sections.! — R- E. Liesegang describes 

 a simple and inexpensive method of preserving large sections of brain 

 by means of embedding in gelatin. The section is placed carefully 

 in a freshly prepared 5 p.c. solution of gelatin, which is gently warmed 

 in order to prevent it from solidifying too rapidly. A further quantity 

 of gelatin is then poured over the surface of the section, and the pre- 

 paration is then removed to a cool place and allowed to solidify. Great 

 care must lie taken to remove all air-bubbles. The best quality of 

 gelatin, that used for the preparation of photographic emulsions, should 

 be used. Attention must be directed to obtaining an even surface on the 

 embedded section. On no account should the preparation be placed in 

 an incubator to hasten the solidifying process. 



* Centralbl. Bakt., 2te Abt., xxix. (1911) pp. 381-4. 

 t Zeitschr. wiss. Mikrosk., xxvii. (1910) pp. 369-74. 



