178 Dynamic Theory. 



and carries it into the inner parts of the body among the combustible 

 cells built largely of carbon like an incendiary carrying a torch into a 

 shop full of shavings. All the iron in the blood is contained in the red 

 corpuscles and this iron, no doubt, contributes very largely to the 

 capacity of the corpuscles for carrying oxygen. For oxides of iron 

 greedily absorb oxygen, which, however, they readily give up to organic 

 substances. And the blood has much greater capacity for oxygen gas 

 than the same quantity of mere water. The business of the red corpus- 

 cle then is to burn up the starch which the chlorophyl cell has gathered 

 from the air. 



The size of the red globules is from -^^ to 9 of a mm. in 

 the adult man. Their shape is disc-like with the sides depressed 

 toward each other. These depressions partly disappear when the globule 

 is charged with oxygen, the sides swelling out, but when the blood takes 

 up carbonic acid they shrink. They are without nucleus, in which 

 respect as well as in shape they resemble the chlorophyl zoospores. 



FIG. 93. 



Red Corpuscles of Blood. They are disc-like, de 

 pressed in the middle, and tend at times to pile them- 

 selves together like dinner plates. 



But they are unlike the* chlorophyl in this 

 respect that their functions do not directly 

 depend on the light, but go on day and night. 

 FlG 93 In the night, or in the continued absence of 



light, the chlorophyl ceases to decompose carbonic acid and to form 

 starch. On the contrary, some of the carbon of its own tissues is 

 absorbed by the oxygen of the air and carbonic acid is thus formed at 

 its expense. Thus it was estimated that a certain square decimeter of 

 green surface lost by consumption ^^ of a gramme of the car- 

 bon of its tissues during twelve hours of darkness, while in a like period 

 of light it gained 3 ^2. grammes. The latter figure is named as 

 the amount of the assimilation, but it is only the net assimilation. The 

 daily expenditure must be much greater than the nightly, and the total 

 assimilation much more than the amount named. The functions of 

 chlorophyl are performed under the stimulus of all colors of lighf, but 

 the yellow rays are the most energetic in such stimulation, and under 

 their influence starch is formed most rapidly. The yellow rays, too, 

 are much the most active in the differentiation of the chlorophyl from 

 the rest of the protoplasm in the first place, and of developing in it the 

 molecular structure that reflects the green rays. The upper surface of 

 the green leaves is by far the most active in the decomposition of car- 

 bonic acid, for the reason that being ordinarily the most exposed to 

 sunlight it contains the greater number of the chlorophyl zoospores. If 



