396 Mr Gustav Mann on the 



the latter exposed to bright daylight. After some time, 

 varying with the temperature of the room and the activity 

 of the threads from three to twenty-four hours, the whole 

 of the Cyanin will have been taken up by the threads. If 

 the latter be examined microscopically, we find the ground- 

 substance of the chlorophyll-bands to have changed from a 

 green to a bluish-green colour, while the oil-globules in the 

 ground-substance have taken on a blue colour. But beside 

 the globules in the chlorophyll bands, many of the micro- 

 somata between the bands have turned distinctly blue, thus 

 revealing their fatty nature. 



If concentrated tincture of Alcanna root be used, it is 

 necessary to leave the Spirogyra material for twenty-four 

 hours in the staining fluid, and then to wash out the threads 

 in distilled water. Tincture of Alcanna root is, however, 

 much inferior to Cyanin, as the alcohol is very apt to dis- 

 solve out the fatty material of the chloroplasts, and to deposit 

 it in large globules at the margin of the bands, or in the 

 general protoplasm. When the oil-globules are deposited 

 along the chlorophyll bands, we get an appearance very 

 similar to the hypochlorin reaction. The globules appear 

 at first to be quite black, but with strong light they are seen 

 to be dark red, with the characteristic microscopical appear- 

 ance of oil-globules. The ground-substance of the chloro- 

 phyll-bands will appear spongy, and stained of a pale pink 

 colour. 



Osmic acid is inferior to both Cyanin and Alcanna, as it 

 is apt to stain the whole cell ; but again we find the oil- 

 globules and the bands stained brownish-black. 



Absorption- Spectra of Chlorophyll. 



After completing the microscopical investigation of 

 Spirogyra, I began the study of the absorption-spectra of 

 chlorophyll. The instrument used was a Browning spectro- 

 scope, and I take this opportunity of expressing my sincerest 

 thanks to Dr Haycraft, who made me familiar with the 

 working of the instrument and with the calculation of wave- 

 lengths in million ths of a millimetre [X] by interpolation 

 curves, after the method described by Dr MacMunn in his 

 work, The Spectroscope in Medicine, page 32. The method is : 



