258 



THE MAINTENANCE OF THE INDIVIDUAL 



filled with fluid. Chlorophyll is a very complex protein, apparently 

 made up of two substances known as Chlorophyll A, having the chemi- 

 cal formula C55H7205N4Mg, and Chlorophyll B, C55H7o06N4Mg. 

 It is found to be somewhat like the hemoglobin of the human blood 

 except that it has an atom of magnesium instead of iron and the 

 property of fluorescence, its color being different in transmitted or 

 reflected light. Chlorophyll in solution, when extracted from the 

 leaf by means of alcohol, appears green as light passes through it, but 

 red when light is reflected from it against a black background. Other 

 pigments are closely associated with chlorophyll, a group of yellow 



pigments called carotins, 

 which give the yellow 

 color to carrots and other 

 fruits or vegetables, and 

 xmithophylls, pigments 

 that help give color to 

 leaves in the fall. 



Numerous experiments 

 have been made to dis- 

 cover how chlorophyll 

 does its work. It has 

 been found that if light is 

 passed through this sub- 

 stance and then broken 

 up by a prism, that part 

 of the light which is 

 absorbed by the chlorophyll may be detected by the presence of 

 absorption bands in the spectrum where the chlorophyll has taken 

 out the light. By this means we learn that the red band of the spec- 

 trum is most active while parts of the blue, violet, and indigo regions 

 of the spectrum are also absorbed. A classic experiment by Engel- 

 mann illustrates this in another w^ay. A filament of an alga was 

 placed in a culture of bacteria which were active only in the pres- 

 ence of oxygen. The filament was then put in darkness until the 

 bacteria had used up all the oxygen present. Then the slide con- 

 taining filament and bacteria was placed on a microscope under a 

 solar spectrum. In a short time the bacteria were found to mass 

 themselves in abundance at the red end of the spectrum and to a lesser 

 extent at the blue end, because at these points more oxygen was 

 given off by the alga, thus indicating activity in starch formation. 



Engelmann's experiment to show the areas in 

 the spectrum most favorable for oxygen release 

 in a green alga. The dots represent bacteria. 



