Size in Relation to Body Surface 163 



all those with contractile vacuoles; and it is circulated 

 by protoplasmic cycloses in many more species. 



Whether oxygen is utilized equally fast by all re- 

 gions of a unicellular body is not known. It is possible 

 that some of the visible structures do not respire at all. 

 The conception has been widely prevalent that nuclei 

 consume oxygen faster than cytoplasms ; this is based 

 on experiments with nucleoproteins and with micro- 

 chemical tests. Child and Deviney ('26) reasoned 

 from the localized effects of cyanides, and Kalmus 

 ('28) concluded from microchemical tests with me- 

 thylene blue, that oxidations might be more rapid in 

 Paramecium at the two ends of the body. The con- 

 tractile vacuoles of various organisms have been sup- 

 posed to be essential in assisting in the supply of 

 oxygen (Rossbach, 72; Degen, '05) and presumably 

 in the localization of the utilization. 



If the functioning of cilia uses up oxygen, then the 

 superficial layers of the body may consume it in higher 

 proportion than the rest of the body. Actually the 

 work done by cilia calculates out to be less than one 

 percent of the oxygen consumption of Paramecium, 

 according to Ludwig ('28a), even allowing only 20 

 percent efficiency. For locomotion and ingestion by 

 flagella, the same relationships hold as for ciliary func- 

 tions. Angerer ('19a) calculated that the work done 

 by the flagella of a bacterium in locomotion amounted 

 to less than one ten-thousandth of the energy obtained 

 by oxidations. 



2. Diffusion of Other Substances 



The limitation of the supply or removal of sub- 

 stances other than oxygen has not been tested in rela- 

 tion to body size. Carbon dioxide, due to its high solu- 

 bility in water, can hardly accumulate under natural 

 conditions. Urea, in concentrations up to 0.14 M, had 



