ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



245 



standard orthochromatic (slow) ; Forbes orthocbromatic (slow) ; Carbutt 

 ortkochromatic (slow) ; Otto Perutz ; Group iii., Lovell colour-differen- 

 tiating ; American spectrum plate. Group iv., Cadett and Neal spec- 

 trum plate (slow) ; Group v., International " Eretbro." 



If sensitiveness to the spectrum were tbe only feature to be con- 

 sidered in the selection of a plate for pbotomicrograpbic work, a plate 

 from Group v. would be cbosen, but tbe general working of tbe plate as 

 well as tbe keeping qualities are factors tbat must be considered. For 

 practical work and keeping qualities tbe autbor found the Cadett and 

 Neal special slow spectrum plate of Group iv. most satisfactory, and 

 used it in the preparation of the spectrographs illustrated in fig. 54, 

 which is a reproduction of spectrographs analysis of some of the common 



Electric arc 



Picric acid . 

 Aurantia . 



Cresoidin . 

 Congo red . 

 Eosin 



Carbol fuchsin 



Hematoxylin 

 Methylen blue 



Green glass 



Methyl green 

 Quinine sulphate 



Methylen blue 



Methyl green 

 Picric acid 

 Picric acid 

 Methylen blue 

 Carbol fuchsin 



Fig. 54. 



stains. Tbe red end of the spectrum is on the left. The principal 

 Fraunhofer's lines are marked. The name of the stain is on the left, 

 while on the right is tbe name of the proper screen for increasing the 

 photographic intensity. To decrease the contrast, a screen of the same 

 colour should^be used ; to increase the photographic intensity a screen 

 of complementary colour should be used. The colour screens were 

 made by soaking a cleared lantern-slide in a solution of the desired 

 stain until the gelatin was saturated, and then by rinsing and removing 

 the surface liquid with a cotton pad. The screen was then dried and 

 covered with a cover-glass, as in mounting a lantern slide. The depth 

 of colour in these screens is dependent upon the degree of concentration 

 of the staining solution rather than upon the duration of soaking. 



