CHAPTER X 

 SIZE IN RELATION TO BODY SURFACE 



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A favorite conception with those who have thought 

 about the limitation of body size, is that somehow 

 the ratio of surface to volume is important. Spencer 

 ('66) for instance, suggested several ways in which 

 surface could be significant in physiological activities. 

 But with one exception no specific instance has been 

 demonstrated in which, for example, the supply or 

 excretion of some particular material proved to be the 

 limiting factor for body size. 



1. Diffusion of Oxygen 



The supply of oxygen might be such a factor. Does 

 a reduction of the tension at which oxygen is supplied 

 to the surface of the body influence the sizes attained 

 by unicellular individuals? The possibility was tested 

 in Colpoda (Adolph, '29). Certain numbers of young 

 individuals were placed upon microscope slides in 

 drops of culture fluid containing high concentrations 

 of food organisms. Half of the slides and drops were 

 placed in a gas-chamber where they were kept for 24 

 hours in an atmosphere of one part of air and three 

 parts of hydrogen. The other half of the slides and 

 drops were kept in a moist-chamber in room air. The 

 frequencies of sizes among the individuals which be- 

 came adults were then measured, and are represented 

 in figure 54. In the low tension of oxygen the individ- 

 uals were all smaller than any in air tension. They 

 were small enough to produce only two progeny each, 

 while the larger control individuals had four progeny 

 each. 



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