306 THE FOEAMINIFEEA 



reducing the strain on the eyes of the worker, as 

 both eyes will be used ; for the monocular form 

 necessitates work with one eye, and if both eyes are 

 not used alternately the injury done by continued 

 work may be great, especially since the selection 

 of specimens is more often carried on by artificial 

 light and with a comparatively powerful illuminant. 

 It is well to bear in mind, in prosecuting this 

 work, the words of Dr. W. B. Carpenter, who him- 

 self devoted forty-five years to microscopical study 

 by artificial light : ' Every microscopist who thus 

 occupies himself, therefore, will do well, as he values 

 his eyes, not merely to adopt the various precau- 

 tionary measures already specified, but rigorously 

 to keep to the simple rule of not continuing to 

 observe any longer than he can do so without fatigue.' 

 Should the worker be obliged to use a monocular 

 microscope, it would be well if he became used to the 

 method of working with both eyes alternately, so as 

 to divide the strain between them. 



The material which contains the foraminiferal 

 shells, and which we wish to sort, is best viewed as an 

 opaque object. A condenser is used to concentrate the 

 rays of light and to illuminate the part immediately in 

 the field of vision ; the lamp found to be most useful 

 is perhaps the ordinary one used by microscopists, 

 which is provided with a shade, screening off all but 

 the rays in a direct line with the condenser and 

 object. In regulating the amount of light when 

 working in this way with the microscope it is better 

 to err on the side of too little rather than too much 



