612 HANDBOOK OF PHOTOGRAPHY 



of the thorax and abdomen during pregnancy can be shown distinctly, and there is a 

 marked difference in the appearance of infrared photographs of primipara and multi- 

 para. In dermatology, infrared photography may be useful in various ways. In 

 cases of eczema, the exterior eczematic appearance does not show in the infrared 

 photograph, while the underlying varicose veins which usually accompany this con- 

 dition are rendered clearly. In lupus cases under treatment by ultraviolet radiation, 

 the whole of the lesion is covered by a scab, and it is impossible to see how the clear- 

 ance is progressing. The infrared rays penetrate the scab, however, and present a 

 clear picture of the healed areas. In ophthalmology, photographs of the iris of the 

 eye by infrared present detail which escapes ordinary photographic materials. Dark- 

 brown pigmented irides appear lighter in tone than blue pigmented irides, and the 

 deeply pigmented trabeculae register lighter than the rest of the iris. If atrophy has 



Fig. 5.4.- — Photograph made on ordinary plates with general illumination. 



begun in the iris, resulting in the destruction of the pigment and replacement by 

 grayish-white tissue, the infrared photograph will show this region of atrophy as 

 darker than the normal tissue of the iris would appear. Abnormalities of the margin 

 of the pupil, not readily visible in black-and-white or color photographs, are clearly 

 recorded by the infrared technique. Since infrared penetrates turbid mediums better 

 than does visible light, it can be used to photograph the iris through a cornea which 

 is so opaque that visual examination is impossible. Infrared photography is of value 

 in the examination of gross specimens, particularly in the case of injected specimens 

 for checking the completeness of the injection without clearing. Since most tissues 

 transmit infrared more readily than visible light, infrared photomicrographs of deeply 

 pigmented tissues and relatively thick histological specimens, such as celloidin and 

 frozen sections, frequently show details which are not discernible in those made by 

 visible light. 



Photography in the Dark. — Since infrared radiation is invisible, it is possible to 

 make photographs in total darkness. Although the ultraviolet is also invisible, it is 

 not satisfactory for dark photographs, because it induces visible fluorescence in many 

 common materials. Infrared photographs can be made in the dark by using radiators 

 which emit only infrared and no visible light or, preferably, by powerful sources of 

 light from which the visible radiations are absorbed by filters which permit the infrared 



