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adding largely to the interest of the subject, also gave the 

 lecturer an opportunity of explaining various details, such as 

 the use of screens, the meaning of absorption bands, and how 

 the eye perceived these effects differently from the photographic 

 plate. Dr. Spitta went on to explain that in the case of 

 bacteria the photographer had mostly to deal with three dyes 

 or stains — viz. Loffler's blue, gentian violet, and carbol fuchsin. 

 Lantern slides showing the method of selecting suitable screens 

 for each of these stains were thrown upon the screen, and the 

 details carefully gone into, and finally photographs of anthrax 

 bacilli, magnified 1,000 diameters, stained with each of the 

 three dyes, were in succession exhibited, illustrating the effect 

 of photography with and without the contrasting screens. It 

 was unanimously admitted that the improvement in detail and 

 definition was most marked. 



The President concluded by thanking Mr. Conrady for his 

 assistance in managing the great spectroscope, and his son, Dr. 

 Harold Spitta, for the manipulation of the lantern. 



Mr. J. Rheinberg, F.R.M.S., said that he had listened to Dr. 

 Spitta's paper with the greatest interest. The contrast between 

 the photographs taken with and without a screen was very 

 remarkable ; but it occurred to him that the contrast between 

 stained bacteria and their background was very great compared 

 with most other microscopic objects, and he would like to ask 

 whether the method employed was adapted to such preparations 

 as sections, where the contrast was less marked and the colour 

 deeper. 



Dr. Spitta said that the question was a most logical one, and 

 not unexpected. In such cases the density of the compensating 

 screen would have to be diminished, and he could assure Mr. 

 Rheinberg that his method had giren very satisfactory results 

 with difficult subjects. 



Dr. Harold Spitta said that he should like to be allowed to 

 confirm the remarks made by the President, his father, from 

 results obtained in his own work. He had recently been engaged 

 in photographing a series of sections of spleen showing bacteria 

 in situ. The members would recognise the difficulty of obtaining 

 contrast in such an object, but by means of some experimenting 

 with screens of varying density, he had obtained very satisfactory 

 results. 



