22 INTRODUCTION. 



methods which are calculated to avoid its chemical alteration. 

 Others, however, have not been successful in repeating his work. 



The substance which Gautier obtained from spinach-leaves oc- 

 curred in the form of small crystals of a dark-green color, which 

 on exposure to light turned brown, then yellow, and finally became 

 colorless. Its composition corresponded to the formula C^H^N/),. 

 The mineral ash consisted of about 1.75 per cent, of magnesium 

 phosphate, traces of calcium and sulphates, while iron was absent. 

 Treated with hydrochloric acid, it was decomposed into phi/lt<>.r<ntthiu 

 and phyllocyanic acid, Gj 9 H^N a O a or CLHj^jOj. This latter is 

 thus a homologue of bilirubin, [C 16 H 18 N 2 O 3 ] 2 , which in turn is 

 derived from hsematin, and is isomeric w r ith hcematoporphyrin. A 

 most interesting relationship between the blood coloring-matter 

 haemoglobin and the vegetable coloring-matter chlorophyl thus 

 becomes apparent, and constitutes a further link connecting the 

 animal with the vegetable world. Recent investigations have 

 shown that a substance can be obtained from chlorophyl, termed 

 phylloporphyrin, which differs only from hsematoporphyrin anhy- 

 dride in containing three atoms less of oxygen, viz., C 32 H 34 N 4 O 2 . 

 Both bodies are thus clearly different oxidation-products of one and 

 the same substance. 



Moderately concentrated solutions of chlorophyl in alcohol or 

 petroleum-ether show seven bands of absorption. The first of these, 

 I, is situated in the red portion of the spectrum between B and C, 

 and is well pronounced and sharply defined on both sides. The 

 bands II, III, and IV are rather indistinct and scattered through 

 the orange-yellow, the yellow and the yellowish-green portion be- 

 tween C and E. From F off, the greater portion of the spectrum 

 is absorbed by the remaining bands, V, VI, and VII, of which V is 

 seen to the right of F, VI most marked about C, while VII occu- 

 pies the extreme violet end. Very concentrated solutions allow the 

 red rays to pass only as far as B, while in greater dilution the green 

 rays likewise appear. Such solutions, therefore, appear green when 

 viewed with transmitted light, while with reflected light they are 

 red and fluorescent. 



When a fresh leaf is similarly examined, a spectrum is obtained 

 w r hich is essentially the same as that just described. There is lack- 

 ing, however, the band that corresponds to the red fluorescent rays 

 of chlorophyl solutions. This is explained by the assumption that 

 the red rays are absorbed by living chlorophyl and transformed into 

 chemical energy. In accordance with this view, we find that when 

 living plants are successively exposed to the various rays constitut- 

 ing sunlight, decomposition of carbon dioxide with liberation of 

 oxygen which, as we shall presently see, takes place in the green 

 portions of every plant whenever it is exposed to sunlight occurs 

 with special intensity when the plant is exposed to the rays corre- 

 sponding to the bands I, II, and III. In this manner, then, chloro- 

 phyl-bearing plants derive their kinetic energy from sunlight, and 



