8 PHOTOGRAPHIC INTRODUCTION 



give the better result. A faint background in the 

 negative nearly always means under-exposure or 

 extreme under-development, and no amount of sub- 

 sequent intensification will cure it. Over-exposure 

 appears as an intense blackening of the background 

 as well as of the bacilli ; the same effect is often 

 produced by extreme over-development with a 

 rightly- exposed plate. 



It occasionally happens that a capital specimen in 

 a bacteriological sense is not sufficiently stained for 

 any coloured glass to produce the necessary contrast 

 to make therewith a good photograph. Advantage 

 then must be taken of the fact that the bacteria rarely 

 possess any details of structure, so that the picture 

 must be under-exposed for the bacteria, and then very 

 freely developed with a strong and well-restrained 

 developer. No amount of development will then 

 bring out details of the bacteria, even if there were 

 any, because of the under-exposure, but the pro- 

 longed development may serve to increase the con- 

 trast. In many cases this will produce results far 

 above expectation. 



The negatives were always developed with 

 Thomas's hydrokinone and soda, until the back of 

 the negative looked very decidedly grey ; 1 gr. of 

 bromide to the ounce of developer was added once 



