162 LIGHT, VEGETATION AND CHLOROPHYLL 



senting 2*7 per cent of the total weight. When treated with a 

 weak acid such as oxaHc acid, chlorophyll loses its magnesium 

 and turns brown; if it is treated with a strong acid it loses the 

 phytol as well. 



Treated with a diastase, chlorophyllase, it loses the phytol 

 but retains the magnesium. Another alcohol then generally 

 replaces the phytol, for example in the course of extraction by 

 alcohol, for this diastase acts rapidly in case of injury. 



When acted on by alkahs, chlorophyll loses its methyl 

 alcohol, and, if it is heated while the reaction takes place, it 

 loses one of its acid radicals at 140° C. and the second at 

 200° C. 



The essential nucleus of the formula is the tetrapyrrol 

 square at the centre of which the magnesium is fixed. It is the 

 same as the nucleus surrounding the iron in the molecule of 

 haemoglobin — a remarkable identity in the fundamental part 

 of these two pigments which are so important in the life of the 

 plant and of the animal; all hfe revolves round this nucleus 

 without which the plant could not assimilate nor the animal 

 breathe. The essential difference between the animal and the 

 plant resides there, for the animal destroys by respiration the 

 reserves accumulated by the assimilation of the plant; he is 

 heterotrophic, feeding himself at the expense of others, while 

 the plant is autotrophic, depending only on itself, and this 

 difference seems connected with the replacement of magnesium 

 by iron! 



This identity does not arise from a mere coincidence; 

 it is an effect of this dependence of animals, which do not 

 seem to be able to synthesize such a nucleus, but use for their 

 essential pigment that derived from chlorophyll, whether they 

 feed on green leaves or on other animals which eat chlorophyll. 



Beside this chlorophyll-^, there are three others — chloro- 

 phyll-^, chlorophyll-c and chlorophyll-^^. They have a very 

 similar composition and the same chemical properties as 

 chlorophyll-^:. Chlorophyll-Z? is distinguished by the fact that 

 an atom of oxygen replaces 2 atoms of hydrogen in the group 

 - CHg on the third atom of carbon, in the upper part of the 



