CHAPTER 8 



Photomicrography 



The easiest way to record a microscopic image is as a photograph. 

 It must be emphasized that such records contribute little to understand- 

 ing. The way to understand what is seen is to draw it, since this forces 

 comprehension on the individual. The writer cannot too strongly urge, 

 on student and teacher alike, that freehand drawing should precede 

 photography. Competent research workers use photography only to 

 demonstrate to others what they themselves have understood. The essence 

 of good photography is to know beforehand what the photograph should 

 look like. The degree to which a photographer succeeds in demonstrating 

 his point is a measure of his technical skill. A camera, particularly in 

 photomicrography, cannot vouch for the truth of an observation. It can 

 only, in extremely skilled hands, record what the observer believes to 

 be the truth. In unskilled hands it cannot even do this, so that some 

 knowledge of underlying theory is prerequisite to practice. 



THE NATURE OF THE PHOTOGRAPHIC PROCESS 



General Description. The recording of images on a photographic film 

 is dependent on the instability of silver bromide. Crystals of this reagent 

 sooner or later decompose to yield metallic silver. They decompose the 

 sooner if exposed to radiant energy from any source but have the peculiar, 

 although not unique, property of being able to absorb such energy in 

 amounts less than is required for spontaneous decomposition. Such crys- 

 tals are naturally less stable than normal crystals and can therefore be 

 decomposed by weaker reducing agents. In this lies the whole basic 

 principle of photography. Sheets of crystals of silver bromide are exposed 

 to light and dark. Those exposed to the light are rendered unstable and 

 form a latent image on the sheet. This image is developed in a weak 

 reducing agent which acts first on the unstable crystals in those areas to 

 which light has penetrated. These crystals having been reduced to 



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