378 NOTICES OF BOOKS AND MEMOIKS. 



to six niiiiutes. The chlorophyll dies, the tissue appearing as if 

 kept for clays in alcohol ; and gradually the other cell-contents 

 follow ; protoplasmic movement, if present, ceases, and the threads 

 break up ; the nucleus, if occupying any fixed position, strays away 

 from it ; the primordial utricle contracts, and loses its property of 

 impermeability by colouring-matters ; the turgidity of the cell 

 vanishes ; and all' the phenomena are presented of hastily induced 

 and irrevocable destruction. 



It is plain that these are not the immediate results of high 

 temperature, since if coloured glasses and solutions are interposed 

 the same general effect is seen, the particular effects varying 

 accordhig to the colour used, e.g., blue light being more powerful 

 than red. With a solution of iodine in carbon -bisulphide, so con- 

 centrated as to transmit no spectrum-influencing rays besides red 

 ones, with a wave-length of -00061 mm.,- none of the described 

 phenomena occur, although at least about eighty per cent, of the 

 heat of the white light is present. With a dark blue solution of 

 sulphuric acid and ammoniac cuprate a quick and powerful action is 

 seen ; as also, if the light be transmitted through a screen of deep 

 green glass possessing little diathermanc3^ 



Experimenting with atmospheres of different constitution, 

 Pringsheim finds that death of the tissue or cell never occurs in 

 media free of oxygen. If, however, experiments be continued 

 beyond measure in other media {e.g., in hj^drogen), phenomena 

 occur attributable solely to the action of heat. If pure carbonic 

 acid be added to the oxygen, there is no photo-chemical action 

 under whatever light be employed. The action is also less 

 vigorous in carbonic acid than in oxygen -holding air. 



The conclusion from all this is " that the destruction of chlo- 

 rophyll by light, in the living plant, is an act of combustion 

 influenced and promoted by light, and stands in no relation to the 

 decomposition of carbonic acid by the plant." 



What becomes of the destroyed chlorophyll was not made out ; 

 it is probable that it passes off directly as a gaseous product of 

 respiration. This much is certain, though, that where the chloro- 

 phyll is attacked by concentrated light, even to the slightest 

 extent, it never recovers, which proves its destruction to be a 

 pathological and not a physiological phenomenon. 



The destructive effects on protoplasm and other colourless 

 constituents of the cell-contents are to be referred directly to a 

 photo-chemical source, the intensity of illumination increasing the 

 affinity of oxygen for the intracellular matters. Now, it is 

 observed that where, as in Nitella, the protoplasm is covered by 

 chlorophyll, its movements are not interfered with even after the 

 expiration of weeks, although where there is no chlorophyll they 

 are speedily terminated. 



Pringsheim thinks therefore that the chlorophyll, so long as it 

 exists in a cell, protects the protoplasm from the injurious effects 

 of sunligiit. Anotlior f auction which lie suggests for cliloropln'll 

 is to diiiiiuish the intensity of respiration by reason of its strong 

 absorption, especially of the chemical rays, and so serve as a 



