T1THONOTYPES IN COPPER. 285 



Buriiig the progress of this decomposition, therefore, more nitrogen, relatively, was 

 evolved towards the close of the experiment than at its beginning. 



822. From this result, therefore, I again infer that the nitrogen emitted by leaves is 

 derived from the decomposition of some azotized body, and not from air mechanically- 

 included in their pores. 



823. The following are the experimental results which I have obtained : 



1st. That the nitrogen comes from the tissue of the leaf itself; because more than 

 three times as much is evolved from bicarbonate of soda as is imprisoned in the struc- 

 ture of the leaf, removable by the air-pump. 



2d. In twelve hours, from bicarbonate of soda, leaves will evolve more than five 

 times their own volume of gaseous matter. 



3d. The quantity of nitrogen in the composition of leaves is sufficient for furnishing 

 all the nitrogen obtained in the gas evolved. From BOUSSINGAULT'S analyses it ap- 

 pears that they contain nearly ten times the required amount. 



4th. The decomposition of some nitrogenized constituent of the leaf is essential to 

 the appearance of the nitrogen : there is no other available source. 



5:2 4. At this stage of the inquiry a remarkable analogy appears between the func- 

 tion of digestion in animals and the same function in plants. LIEBIG has shown how, 

 from the transformation of the stomach itself, food becomes acted upon and is turned into 

 chyme : an obscure species of fermentation, brought about by the action of nitrogen- 

 ized bodies. So, in like manner, in plants, the decay of a nitrogenized body is inti- 

 mately connected with the assimilation of carbon; for, as I have stated, the process 

 here under discussion is a true digestion and not a respiratory process. And as there 

 are facts which seem to show that the primary action of the light is not upon the car- 

 bonic acid, but upon the nitrogenized ferment, the decomposition of the gas ensuing 

 as a secondary result, if it not probable that CHLOROPHYL is the body which in veg- 

 etables answers to the CHYLE of animals? The oxygen, which disappears during the 

 decomposition of carbonic acid, disappears to bring about the eremacausis of the nitro- 

 genized body. And have not the gum, the starch, the lignin, and other carbonaceous 

 constituents of plants, all originally existed in and passed through die green stage t It 

 is the quality of radiant matter to determine the position of atoms and the grouping of 

 molecules ; and for this the sun, the great organizer, the great life-giver, from age to 

 age furnishes his unfading beams. That analogies like this between the. organic func- 

 tions of plants and animals in reality exist, we might reasonably suppose ; they are 

 agreeable to the general plan of nature. 



Note on the Tithonotype. 



825. IN chapter xiv. I described a process for obtaining tithonotypes, or copies of the 

 surface of Daguerreotypes, by means of gelatine. 



826. A very important improvement on that process an improvement which, indeed, 

 has brought it almost at once to perfection has been effected ; this is, To copy the sur- 



AA 



