ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 123 



the butter sample was placed in 10 c.crn. sterile water and kept at 25° C. 

 This was then thoroughly mixed and allowed to cool. The fat having 

 separated, "1 c.crn. was taken and mixed with nutrient gelatin, usually 

 2 p.c. lactose gelatin, and plated out in the usual way. The colonies 

 were then counted, and subcultures made in different media. For the more 

 ready estimation of gas-forming organisms, the solidified inoculated 

 gelatin in the Petri dish was covered with a thin layer of sterile gelatin. 

 The little gas-bubbles were then easily seen. The author found that 

 undesirable flavours and aromas were in most cases due to the action of 

 micro-organisms, working either in the ripening cream or in the made-up 

 butter. Such organisms may be either bacteria, yeasts or moulds. A 

 good-flavoured butter containing undesirable contaminations will soon 

 become objectionable. The bacteriological tests were not found to agree 

 with the judge's awards. 



Metallography, etc. 



Dichroiscope.*— This instrument (fig. 23), made by Swift & Son, 

 is for the accurate comparison of the different colours of dichroic 

 minerals. It is extremely useful for distinguishing coloured gems from 

 glass imitations. 



Fig. 23. 



Penological Examination of Paving Sets.f — J. Joly gives the 

 following method for determining the proportions of hard and soft 

 constituents in rock. The thin rock-section is placed in the Microscope, 

 and using a low power and low eye-piece the image of the field is pro- 

 jected into a ground-glass screen above the eye-piece, any of the usual 

 photographic apparatus being used. The ground glass is turned rough 

 side up. Upon this is placed a transparent divided scale prepared as 

 follows. A piece of logarithmic paper (divided to square millimetres, or 

 square tenths of inches) is placed in contact with a sensitive plate in a 

 photographic printing frame, and printed off by contact in the usual 

 manner. The result is a negative, having the divisions appearing as 

 clear lines on a dark background. This negative may be used, or a 

 positive printed from it. The transparent divided scale is placed face 

 downwards upon the ground-glass. We now have an image of the field 

 traversed by the lines upon the scale. On the back of this scale, the 

 outline of any particular constituent is traced by an ordinary writing 

 pen and ink. This done, the divided plate is lifted off, and holding it 

 up to the light the number of square millimetres, or square centimetres, 

 are estimated as contained within the ink outlines. The whole circular 



* Swift's Catalogue, 1901, p. 40. 



t Proc. Roy. Dublin Sop., x. (1903) pp. C2-92 (4 pie.). 



