664 SUMMARY OF CURRENT RESEARCHES RELATING TO 



intervention of any complicated mechanism such as is necessary from the 

 usual position behind the camera. It may be convenient to examine the 

 image with a small telescope or opera-glass. 



Photomicrography with High Powers.* — Dr. 0. Israel draws attention 

 to the photomicrography of fresh objects, especially of vegetable micro- 

 organisms in their natural condition, by the application of high powers and 

 the use of good bromide gelatin plates. 



For most microbes it is necessary to use very narrow diaphragms in 

 order to reproduce the fineness of their lines with sufficient clearness ; 

 and as thereby much light is lost, long exposure becomes necessary. Hence 

 also a very stable apparatus is a sine qua non. The duration of the expo- 

 sure is dependent on the clearness of the microscopic picture, and this in its 

 turn depends on the source of light, the objective, and the size of diaphragm. 



Diffuse daylight gives the best light, and for high powers and immersions 

 a condenser is either desirable or necessary. Dry, water, and oil-immersion 

 lenses are all applicable, though the best results were obtained with Hart- 

 nack's immersion ii. with correction. 



It is of great importance that the object to be photographed should be 

 very thin, in order that the parts above or below the plane in focus should 

 not detract from the clearness of the picture. 



For over-exposed pictures the author recommends the addition of a 

 few drops of a concentrated solution of bromide of potassium to the iron 

 developer, and this does not interfere with any subsequent treatment with 

 cyanide of silver. Evidence of the efficacy of the method is given by the 

 prints of negatives of micro-organisms and of other fresh objects, among 

 which may be mentioned striated muscular fibre in salt solution. 



Crookshank's * Photography of Bacteria ' and ' Manual of Bacteriology.' 

 — The intention of Dr. E. M. Crookshank's 'Photography of Bacteria 'f 

 will be best explained in his own words : — " It might appear ill timed to 

 publish photographs of bacteria when the apochromatic objectives, which 

 promise to be of such great advantage in photomicrography, have just 

 been introduced. I only wish, however, to illustrate results obtained with 

 ordinary objectives, and to demonstrate that photography may be employed 

 with success to represent preparations of bacteria even under conditions 

 unfavourable for photography. There has been no desire to produce a 

 series of feats in photomicrography ; but on the other hand, I am anxious 

 to encourage the attempt to make photography subservient to bacteriology. 

 Those who would aim at the former should select difficult test-diatoms as 

 their subject, and endeavour to equal or surpass the photographs taken by 

 Dr. Woodward, of America. 



" The preparations to be photographed were selected without any 

 reference to the staining reagents which had been employed, and in some 

 cases photographs are given which were purposely taken of bacteria so 

 faintly stained, as to be demonstrated under the Microscope with difficulty. 

 " It is hoped that these photographs will be useful as supplementary 

 illustrations to my ' Manual of Bacteriology,' while the accompanying letter- 

 press may serve as an introduction to the methods employed in photo- 

 micrography." 



A second edition of the author's ' Manual of Bacteriology ' J is also 



* Virchow's Archiv f. Path. Anat. u. Physiol., cvi. (1886) p. 502. 



t Crookshank, E. M., 'Photography of Bacteria,' xx. and 64 pp., 6 figs, and 

 22 plates of photographs with explanations, 8vo, London, 1887. 



t Crookshank, E. M., 'Manual of Bacteriology,' 2nd ed., xxiv. and 439 pp., 137 figs, 

 and 29 pis., 8vo, London, 1887. 



