INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 681 



•which is not applied to the coloured plasma of the Diatomaccfe alone, 

 but also to that of all the Algfe in general, whatever their colour. 



The endochrome of the Diatomace<\} does not give up its pigment 

 either to cold or boiling water, but after rather prolonged maceration 

 it is completely decolorized by cold alcohol, and the latter acquires 

 a brownish-green colour of greater or let^s intensity. 



If the plasmic masses of the frustules ai-e examined after macera- 

 tion in the alcohol, they will be found unchanged in form. They are 

 still, as before, either laminae or granules — they have only lost their 

 colour. The plasma, without any sensible loss of form and without 

 diminishing, so to say, in volume, has yielded up all its pigment to 

 the alcohol. From this we are led to conclude that the colouring 

 matter impregnates the plasmic masses contained in the frustules, in 

 the same way as chlorophyll impregnates the chlorophyll-bodies in 

 the higher plants. 



It is by maceration in alcohol that the pigment is extracted from 

 Diatomacese. It is first of all necessary to j^rocure diatoms free from 

 Oscillatoria or any other kind of alga ; wash them several times in 

 fresh water, if they are marine species, and afterwards in distilled 

 water ; let them drain for some time, and dry them rapidly between 

 sheets of filtering paper. The diatoms thus prepared are then 

 immersed in a volume equal to their own of 90 per cent, alcohol, and 

 left to macerate protected from the light. As soon as the diatoms 

 experience the contact of the alcohol they take a very distinct green 

 colour and the alcohol immediately becomes a golden yellow. 



After six or eight days the alcohol has taken a dull green colour 

 more or less inclining to brown, and the diatoms have in a great 

 measure lost their colour ; but it is only after a month or more of 

 maceration that the plasma becomes completely colourless. Filtered 

 after eight days of maceration we obtain a concentrated alcoholic 

 solution of the pigment. 



2, Historical. — M. Niigeli * was one of the first to mention the 

 colouring i)rinciple of the Diatomaccfc and describe its chemical 

 properties. He considered this colouring matter to be simple, and 

 gave it the name of diatomine, which wc will preserve, because of its 

 analogy to chlorophyll, Avhich is itself a compound body. 



However, before bim, M. de Brcbissonf first, and later on 

 Kiitzing, J had remarked that " Melosira becomes green w'hen dried 

 upon iiaper." Kiitzing had moreover proved tliat the brown coh)ur- 

 ing principle becomes green under the influence of hydrochloric acid, 

 and that alcohol removes from the plants a green pigment resembling 

 chlorophyll. 



In 18G7 M. Askenasy § had succeeded in isolating, in an imperfect 

 manner, it is true, the two colouring princii)les of diatomin, and liad 

 recognized their principal chemical and optical properties. Although 

 theio experiments were not at the time considered as conclusive, they 



* ' Gathingcn ciiizcU. Algcn,' p. 7. 



t Biol)ia.-<on iiml (todcz, ' Algiics dcs Environs (h> Falniso,' \K\vt, p. 11. 



X ' HncMllftric'ii.' p. T^. 



§ "Biit. /,. Kiimt. (kr Clilninphylla-FiirbstunV," 'But. Zcit.,' July, IMiT. 



