1885.] 



MICROSCOPICAL JOURNAL. 



31 



modification of Dr. Roy's, and sliding 

 microtomes ; Verrick's microscopes ; 

 large and medium stands; litho- 

 graphs, plain and colored, of the silk- 

 worm moths, caterpillars, internal 

 organs, and figures of the disease 

 corpuscles ; figures of many figured 

 ferments found in beer and wine ; also 

 drawings of the vinegar process; 

 while adjoining will be seen the mode 

 of examination of silk-worm moths, 

 as carried out on a large scale, with 

 much that is interesting in this for- 

 tunately recovered silk-worm rearing, 

 the loss of which would have proved 

 most serious to France ; and close to 

 this exhibit is a model apparatus and 

 drawings of the mode of Pasteurizing 

 wine by one of the large wine mer- 

 chants — M. Houdart. Besides what 

 we have enumerated, there are a few 

 photomicrographs from negatives by 

 Dr. Roux, which have a special claim 

 for notice. 



We had the pleasure of examining 

 two small negatives about the size of 

 a sixpence, which bore enlarging up 

 to the ordinary lantern size of trans- 

 parencies, and to the fidelity of these 

 we can testify. These negatives go 

 far to support what is not generally 

 allowed — that better negatives of bac- 

 teria and very minute objects can be 

 produced without the eyepiece, by- 

 obtaining more perfect small nega- 

 tives, than by original large direct 

 negatives. There is, of course, the 

 additional trouble of copying and en- 

 larging ; but we must not let this stay 

 our hand when we are seeking for the 

 best work. The plan adopted by Dr. 

 Roux, which is one to meet rapid 

 laboratory work, was to fix a small 

 camera or cell to the eye end of the 

 microscope containing the little gela- 

 tino-bromide plate, the position of the 

 focus and the image having been pre- 

 viously determined by placing a piece 

 of plain glass in the slide, and on its 

 upper surface a few scales of moth or 

 butterfly. These are brought into 

 focus by a low-power objective used 

 as a focussing-glass, and the image of 

 the object on the stage of the micro- 



scope and the image of the scales are 

 made to coincide. Hence, by with- 

 drawing the little camera and insert- 

 ing the focussing objective, the focus 

 of any object on the stage can be made 

 to occupy the exact position of the 

 scales on the transparent glass. In 

 other words, the focus of these and 

 the new image are coincident, and, 

 the surface of the small gelati no-bro- 

 mide plate falling exactly on to the 

 same plane, there can be no error 

 through the different thickness of the 

 glass plate, as the focus of the scales, 

 the image of the object, and the sen- 

 sitized surface are in one plane. 



The illumination is by a small 

 parafiine lamp. The arrangement is 

 s i m p 1 y removal of the eyepiece, 

 insertion of the focussing objective, 

 and then the fixing the little camera 

 into position. There is no reason 

 why a somewhat larger camera may 

 not be used, and a rather longer and 

 larger tube adapted to the working 

 microscope, or the camera maybe in 

 part supported, as suggested by Dr. 

 A. C. Mercer, of Brooklyn, U. S., 

 by a strut from the stand of the mi- 

 croscope. For the most perfect work 

 it would, perhaps, be preferable that 

 the camera should be only loosely 

 connected with the eye end of the mi- 

 croscope, though otherwise a fixture. 

 The plan of development adopted by 

 Dr. Roux was that, we believe, recom- 

 mended by Colonel Stuart Wortley, 

 of soaking the plate in weak ammo- 

 nia before applying the pyro., and 

 then adding ammonia, as required, to 

 bring up the image. We would 

 strongly recommend examination of 

 these exhibits, and we must again re- 

 mind those disposed to aid photo- 

 graphically in the study of the bacte- 

 ria, that patience — the common vir- 

 tue of the photographer of the infan- 

 tile world — will be largely requisi- 

 tioned, even under favorable circum- 

 stances. 



There are other photomicrographs 

 in the gallery of the Albert Hall ; and 

 in Dr. Cheyne's laboratorv will be 

 seen some of Dr. Koch's photomicro- 



