PHYSIOLOGICAL STUDIES ON PLANARIA. 



III. OXYGEN CONSUMPTION IN RELATION 

 TO AGE (SIZE) DIFFERENCES. 



L. H. HYMAN, 

 HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO. 



I. REVIEW OF LITERATURE. 



The present paper is a report of some determinations of the 

 rate of oxygen consumption of small (young) as compared with 

 large (old) planarians belonging to three different species. That 

 the metabolic and other activities of small individuals are more 

 rapid than those of large individuals of the same and different 

 species is so well known from a number of independent investi- 

 gations that further evidence appears almost superfluous. The 

 majority of these investigations, however, deal with vertebrates, 

 where a certain difficulty inherent in the nature of the material 

 is encountered. This difficulty centers about the impossibility 

 of finding a proper unit for comparison of animals of different 

 sizes. Among the warm-blooded vertebrates, the metabolic 

 rate has commonly been reckoned per unit of surface area on the 

 necessity of taking into account loss of heat by radiation. But 

 leaving out of consideration the difficulties of accurately measur- 

 ing the surface, over which proceeding a controversy of long 

 standing exists, the surface method of comparison is more or 

 less meaningless in the case of cold-blooded animals. Nor is the 

 method of comparison of metabolic rate per unit weight free 

 from objection. A considerable part of the weight of the verte- 

 brates and the higher invertebrates consists of skeletal material, 

 connective tissue, fat, etc. The metabolic rate of such material 

 must be relatively low, and further its proportion to the total 

 weight must be different in animals of different sizes; neverthe- 

 less, these factors have not been considered in any of the re- 

 searches on the subject, nor, as far as I am aware, has anyone 



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