146 PHOTO -MICR(3G"RAPHY 



There is no special difficulty otherwise than to obtain sufficient contrast in taking 

 photo-micrographs of bacteria when they are stained. Hydroquinone produces dense 

 pictures which are always necessary, especially when lantern slides are required, for no 

 background, unless it be of some specific nature, is needed, and the bacteria on clear glass 

 look much better on the screen than when they are shown on a dirty white background. 



When taking a photograph of living bacteria, such as the clumping of the typhoid 

 germs in Widal's method of diagnosis, much difficulty may be experienced in getting 

 a photograph at all. It is best then to take advantage of diffraction effects and to 

 close the iris, what would be otherwise considered an undue amount. By this means 

 a faint " standing-out " effect is produced which enables the bacteria to show suffi- 

 ciently for the purpose, provided the exposure be short enough to prevent choking 

 effects, and yet long enough to give a sufficiently dense background. We found 

 about ten seconds with a subdued light and using a Jth apo. about correct. A 

 vertical apparatus must be used, about which we have already spoken. 



It should be distinctly remembered that when photographing stained bacteria the 

 iris diaphragm Hliould 7iever be closed, and a full-sized cone of light always employed, 

 otherwise white diffraction lines will appear around the organisms. At times we have 

 thought that a 1-35 achromatic substage condenser gave better results, especially 

 when photographing bacteria with flagella. Examples of this type of work are 

 shown in Figs, i, 2, 3, Plate IV., and Figs. 7. 8, 9 and 10, Plate V. 



The story of photo-micrography is now told — at least, so fa,r as it relates to the 

 experience of the author ; but before he lays down his pen he wishes to point out to. 

 his readers the desirability of never passing a comment upon efforts of their own or 

 those of others without directly comiJaring such, luith the work of the best of experts. 

 Comments without such comparison are often wrong, and may be most misleading. 

 The true spirit of the photo-micrographer should be one of " effort," ever remembering 

 the old adage, " If at first you don't succeed, try, try again." " Ever learning," then, 

 must be his motto, and if by fair criticism founded upon the works and not the ivords 

 of others he is shown his shortcomings, he must not take umbrage or be discouraged, 

 but once more try again. 



Mr. Wall— a well-known authority on such matters— and is worthy of note. Coat patent plate with a 2^ per cent, solution 

 of albumen. When dry, pour over 170 minims of an 8 per cent, solution of gelatin. Level and allow to dry. 



For Yellow Screens. — Soak in the following solution: 20 grains of picric acid dissolved to saturation in absolute 

 alcohol, two ounces of water and a little ammonia. 



For Red Screens. — Soak in a i per cent, solution of crysoidiue. 



For Orange Screens. — Soak in a i per cent, solution of aurantia. 



For Green Screens.— Soak in a i per cent, solution of naphthal green, acid green, or methyl green. 

 For Violet Screens.— Soak in a i per cent, solution of methyl violet. 



