ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 755 



often necessary, at the risk of concealing its inclosed substances, to 

 employ very dilute methyl-violet ; one drop of a solution containing 

 l-10,000th or even only l-50,000th poured over the preparation is 

 sufficient in many case*. 



This solution can be made to act either immediately on the proto- 

 plasm or even after treatment with osmic acid. In the latter case 

 there is still a coloration. It may be seen in Clathrocystis roseo- 

 persicina, the Euglence, several nudo-flagellate organisms, and in the 

 cells of the Phanerogams. Certes, who has successfully applied this 

 reagent to the microscopical analysis of water, recommends its appli- 

 cation mixed with diluted glycerin. He says * : " Precautions must 

 be taken to make the action of the glycerin very slow, so as to avoid 

 the shrivelling of the tissues. In these conditions the absorption of 

 the colouring matters is better effected ; the organisms remain trans- 

 parent, and if we wish to preserve specimens, the glycerin constitutes 

 a preservative medium, and keeps the organisms from evaporation." 



Whilst methyl-violet kills the protoplasm at the same time that 

 it colours it, very weak aqueous solutions of anilin-brown, fuchsin, 

 and eosin, colour the protoplasm without killing it immediately. 

 Organisms have been seen to live many hours after having been 

 coloured by these substances. 



Koch has used an alcoholic solution of eosin to kill and colour a 

 reddish pink the protoplasm of Sarcina, Bacterium, and Bacillus. 



The aqueous solution of cyanin or quinolein blue, whilst pene- 

 trating the living protoplasm, condenses the colouring matter in 

 sufficient quantity for its tint to be perceptible. Certes f was able ,to 

 show the members of the Zoological Society of France some living 

 infusoria which he had coloured many hours previously by means of 

 cyanin and anilin-brown, also called Bismarck-brown. 



These results are important : by taking them into consideration, 

 in the future we may be able to study, on the living subject, the pheno- 

 mena of conjugation and reproduction in the Algae and the Infusoria, 

 instead of being, as hitherto, confined to the study of the organisms 

 killed in different stages of their evolution. 



Nucleus. — Generally speaking, the substances which colour the 

 protoplasm, iodine, fuchsin, and carmine, also colour the nucleus, 

 which absorbs the colouring matter in greatest quantity. It can be 

 further studied, moreover, by means of particular reagents. 



Subjected to the action of osmic acid, the nuclei become black. 

 Iodized glycerin makes them yellow. According to Treub,f methyl- 

 green colours very dark green those nuclei which are not in process 

 of division, and pale green those which are dividing, because in reality 

 this reagent only colours the chromatin in the nucleus. 



In his researches on the division of cells, Strasburger § employed 

 the anilin colours with 1 per cent, of acetic acid as reagents for the 

 nuclei. The very deep colouring which they take in these con- 



* Comptes Eendus,'l4th June, 1880. 



t Bull. Soc. Zool., 22ad February, 1881. 



X Arch. Neerland., xv. (1880). 



§ 'Zelibildung und Zelltheilung,' 1880. See this Journal, i. (1881) p. 621. 



