INTRA VITAM COLOR REACTIONS IN NEMAS 123 



permanency be disregarded. Furthermore, as already hinted, color- 

 less compounds may be used if in the course of the metabolism they 

 are converted into colored compounds. The results of recent studies 

 of dyes as chemical indicators come into play, and give valuable evi- 

 dence in determining acidity and alkalinity. 



I am almost ready to express the opinion that a small army of in- 

 vestigators should be engaged on the problems opened up in this way. 

 The equipment needed by the investigator is as follows: (1) He must 

 be a good microscopist, versed in physiology, cytology, and histology. 

 (2) He should be conversant with the chemistry of the coal-tar com- 

 pounds, not so much from the viewpoint of the maker of dyes as from 

 that of the broad-minded chemist, freed from the economic domina- 

 tion of the dye industry, for, as before remarked, fugitive dyes, and 

 even colorless compounds, are possible factors in such investigations 

 as are here under discussion. (3) He should have a working knowl- 

 edge of nemas. 



ILLUMINATION 



In order to distinguish with accuracy among intra vitam color re- 

 actions it is necessary to be very particular about illumination. The 

 most perfectly corrected lenses must be used, both as condenser and 

 objective, and the light used must be as nearly white as possible. The 

 best source of light known to me for these researches is bright sun- 

 light reflected from a plane, matte, white reflector. The reflector 

 should be several feet across, and placed at a distance from the micro- 

 scope several times its own diameter. It should be universally ad- 

 justable, so that it can be set to reflect a maximum of light to the mir- 

 ror of the microscope, all the better if it is heliostatic. A good 

 surface for the screen is made by whitewashing a rather finely woven 

 cotton cloth. 



The best optical arrangement I have tried is the use of one apo- 

 chromat objective as a condenser for another apochromat. I have 



been USing With s ?uare c^r ff / ass ^ u ^ eo^ry/aiss_ 



success a 2 mm. 

 apochromat as a 

 condenser for a 2 



mm. Or 1.5 mm. Fig. 7. Microscope slide used for intra vitam examinations as indicated 



apochromat ob- 

 jective. These precautions are necessary if fine color distinctions are 

 to be made with the greatest possible accuracy. If these precautions 



