456 E. EAY LANKESTER,. 



iuteiiial chemical activities of the celisj upon a knowledge of 

 which a true physiology must be based. 



Colour and Absorption Spectra of Chsetopterin. — 

 The freshly-prepared alcoholic solution of Chsetopterin (as 

 obtained from a fresh specimen of the mid-region of the 

 animal's body) is of a blackish green colour by transmitted 

 light (see PI. 35, fig. 6), and shows a powerful red fluorescence, 

 resembling in colour that of an alcoholic solution of chlorophyll. 

 This solution is found to be neutral in reaction. When 

 examined with the spectroscope it shows four detached absorp- 

 tion bands, the position and intensity of which are represented 

 in Dr. Benham's drawing (PI. 34, fig. 5, uppermost spectrum), 

 but are more exactly shown in the valuable observations kindly 

 made for me by Professor Engelmann, and recorded in the two 

 charts on PI. 36. 



When the neutral solution of Chsetopterin is rendered acid 

 by a very slight addition of HCl, it assumes a fine indigo-blue 

 colour, as shown in PI. 35, fig. 7. The absorption spectrum is 

 still four-banded, but the position of all the bands is shifted, 

 notably of the two in the blue. Dr. Benham's drawing in 

 PI. 34, fig. 5, shows this; the exact position and intensity of 

 the absorption is shown by the two dotted lines in Professor 

 Eugelmann's chart, PI. 36. Professor Engelmann finds in a 

 sufficiently thin layer of the coloured liquid a faint'* fifth" 

 band at wave length 500, indicated by a dip and rapid rise in 

 the curve traced by the upper dotted line of his chart. In a 

 layer of greater thickness (recorded by the lower dotted line) 

 the differentiation of this band from the absorption on either 

 side of it is (as in Dr. Benham's drawing) inappreciable, ex- 

 cepting by the most careful measurement and comparison. 



The acidulated solution may now be rendered alkaline by 

 addition of KHO or NaHO, when it assumes a bright lemon- 

 green colour (PI. 35, fig. 8). The alkaline solution still 

 exhibits four detached absorption bands, but they are very 

 much in the same position as those of the neutral solution. 

 The difference in the colour of the neutral and the alkaline 

 solution is due, as is shown very clearly by Professor Engel- 



