502 



EXPERIMENTAL PHARMACOLOGY 



records. A cheap lens or one usually supplied with an 

 ordinary view camera will not do this work. 



The average time required for an exposure of a plate in 

 the light of the laboratory (from 9 A. M. to about 2 or 3 p. M.) 

 will be about twenty to twenty-five seconds. The plate is 



Board attached 

 to ceiling 



- Arc light 



Fig. 387. Method of suspending an adjustable arc light above the operating table. The 

 lamp should be 2 or 3 feet above the field of operation. 



then taken into the dark room and developed. For lantern 

 slides the negatives should be thoroughly developed and 

 should be considerably darker than is required for making 

 ordinary paper prints. If only a small amount of work 



