44 



LIMITATIONS. 



Photography has its limitations. The time of exposui*e can not be 

 accommodated to a field unequally illuminated. A man ten feet from the 

 camera and a background of forest and hills from a hundred to a thousand 

 feet away can not all be in correct focus at once. Undesirable and imma- 

 terial parts of the field will be taken with the same fidelity as the parts 

 wanted. Photomicrography shares all these limitations. With skill they 

 can be reduced to a minimum. By repeated exposures of the same field 

 all parts wanted can be presented in correct focus and together in their 

 true relationship. Fig. 5 was focused for the centrosome in the larger 

 cell; Fig. 6 for the centi'osome in the smaller cell. By the use of a special 

 stage, objects can often be tilted so as to bring related points into the 

 same plane. When one side of a field is lighter than the other something 

 can be done by stopping the development at proper stages, washing 

 the negative off and developing the exposed parts by a local application 

 of the developer. Immaterial parts can be cut out by the application of a 

 reducing agent to the negative or the positive, or by matting out in the 

 process of printing. Much has been said against the use of reduction, 

 intensification, retouching or even spotting out, and many inartistic, not 

 to say ugly, prints have been made that might easily and without damage 

 to fidelity have been made tolerable, if not beautiful. By the adjustment 

 of the light, by the kind of light used, by the character of the developer, 

 by the intensity of development, by the time of exposure and by the 

 quality of the plate, two prints of the same object can be made to tell 

 different tales. Photomicrography is not a means of compelling men to 

 tell the truth; no such means has ever been discovered; the usual bounty 

 for veracity is still to be had at the old stand. Clumsily practiced it tells 

 nothing; it is reliable when the photomicrographer is both truthful and 

 capable. There is no more reason why it should be compelled to tell 

 immaterial stories while it is telling material ones than that any other 

 witness on any other stand should be. I have, notwithstanding all this, 

 always followed the rule never to cut out or reduce anything whatever 

 from the material portion of the field. I have often hunted for hours 

 to find a section free from defects which told exactly the same story 

 that another one told, the defects of which I could have removed harm- 

 lessly and easily. 



