ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 969 



work with monochromatic light where the greater intensity compensates 

 for the light absorbed. It also possesses the advantage of compara- 

 tively lower heat, as it can be brought very close to the object. It is 

 also very pure, which proves useful with complicated stains, and it 

 is very uniform. 



Dr. Van Heurck, it will be remembered, has already published * 

 the opinion that " the incandescent electric light supplies the illumi- 

 nation par excellence which the microscopist req[uires." 



Clayton and Attout-Tailfer's Isochromatic Plates for Photo- 

 micrography.l — The different colours of the spectrum are, as is 

 known, far from having the same reducing action on silver salts ; 

 there exists, in fact, an antagonism between their luminous intensity 

 and photo-chemical action. It is thus that objects coloured yellow 

 or orange (which are luminous colours) produce almost black images, 

 whilst objects coloured blue or violet (which are dark colours) give 

 pale and almost white tones. 



Dr. E. Van Ermengem has obtained some excellent photo-micro- 

 graphs by using the isochromatic plates of Clayton and Attout- 

 Tailfer, of Paris, which in the reproduction of the Bacteria for in- 

 stance do not necessitate any special device for illumination, or the use 

 of coloured glass even when the objects are stained red with fuchsin. 



According to Dr. Van Ermengem the scientific application of 

 photography is likely to derive the best results from these plates. 

 The methods of staining so much used at present in micrographic 

 research have undoubtedly contributed to restrict the use of photo- 

 graphy even where it would have been most useful. In bacterio- 

 scopical researches especially, it has been very difficult hitherto to 

 get suitable images of certain bacteria, such as B. tuberculosis, which 

 cannot be coloured with brown stains. The same was the case 

 with preparations treated with methyl-blue or fuchsin, the most 

 usual staining reagents. The isochromatic plates, however, enable 

 excellent photographs of these different preparations to be obtained 

 with equal facility. Their manipulation does not differ from that of 

 the ordinary plates, and their sensitiveness is very great, though 

 possibly less than that of the bromo-gelatin plates of Van Monck- 

 hoven. The sensitiveness of the plates to coloured light is due to 

 the impregnation of the sensitized layer by a very weak solution of 

 eosin. All the compounds do not, however, give good results, and 

 what kind of eosin ought to be used is not yet decided. 



Error in Photographing Blood-corpuscles.j— A note on a pos- 

 sible source of error in photographing blood-corpuscles, by G. St. Clair, 

 communicated to the Birmingliam Philosophical Society, is a fruitless 

 attempt to explain as an optical illusion Dr. Korris's asserted dis- 

 covery by the aid of photograjihy of a third kind of corpuscle in 

 mammalian blood. 'J he author invokes the principle of the forma- 



* See tliis Journal, ii. (1882) p. 418. 

 t Bull. Boc. Belg. Micr., x. (1884) pp. 170-2. 

 X Niiturc, XXX. (1881) pp. 4U5 and 517. 

 Ser. 2.— Vol,. IV- 3 S 



