NUTRITION 51 



the carbon atoms of the carbon-dioxide. Light rays of 

 definite wave-lengths are the force employed by the living- 

 protoplasm to separate the carbon, hydrogen, and oxygen 

 atoms and to reunite them into another and more complex 

 molecule than either carbon-dioxide or water. Chlorophyll 

 is the pigment which absorbs these light rays. Living pro- 

 toplasm is the only agent yet known which can combine 

 these tw r o universally occurring and extremely stable com- 

 pounds, carbon-dioxide and water, into food for living 

 beings. 



CHLOROPHYLL 



Chlorophyll is a pigment, more properly a mixture of two 

 or more pigments, of unknown chemical composition, proba- 

 bly nitrogenous, extremely unstable, lifeless, but enclosed in 

 the living protoplasm, usually in definite living organs of 

 the protoplasm called plastids or chromatophores. In the 

 cells of the lowest algae, the Schizophyceae, the peripheral 

 layers of protoplasm contain a mixture of blue and green 

 pigments which give to them their peculiar blue-green or 

 olive-green hue. Whatever may be the function of the blue 

 pigment, soluble in cold water, it is accompanied by a green 

 pigment, or a mixture of pigments which is green, of similar 

 composition and the same functions as chlorophyll. Higher 

 algae consist of cells more differentiated in that the chloro- 

 phyll is confined to definite parts of the peripheral layers of 

 protoplasm, in bodies possessed of denser structure than the 

 rest of the protoplasm, apparently of a living framework 

 between the parts of which the chlorophyll, as a dense and 

 oily liquid, is enclosed. With further division of labor in 

 the cell the size of the chromatophores is decreased, their 

 numbers are increased, and the enclosed pigments become 

 denser. By these means the effectiveness of the chromato- 

 phores themselves is increased, their smaller size admits of 

 their moving about in the cell, thus enabling them to oc- 

 cupy different positions at different times, but at all times 

 the most advantageous ones; at the same time, a smaller 

 proportion of the cytoplasm is limited to the work of food- 

 manufacture. 



