348 HARVKV M. SMITH. 



Since the absorbing surface of a cell increases only twice as 

 fast as the radius, while the mass to be nourished by absorbed 

 material increases four times as fast, it follows that there is a 

 definite size limit to cell growth; and further it is evident that 

 the absolute size attainable by any given cell is inversely propor- 

 tional to its rate of consuming the material absorbed. In other 

 words, a sluggish cell may absorb the relatively small amount of 

 material needed for its activity through a smaller surface than a 

 more active cell, with its greater requirements of material; or 

 the sluggish cell could grow to a larger size than the active one 

 and still get sufficient material through its surface. If this is 

 true, then one may reasonably expect a sluggish animal to have 

 larger cells, while a more active animal would require smaller 

 cells. 



The research described in the present paper was started with 

 the idea of obtaining some experimental data which might indi- 

 cate whether the assumption stated above is true, and therefore 

 whether the size of cells might be of fundamental importance in 

 the activities of an animal. The Amphibia were chosen for 

 experimental material because they have quite large cells which 

 can be measured with less error than smaller cells, and because 

 the Amphibia are known to vary quite widely in both cell size 

 and activity. 



Gulliver (1875) published measurements on the blood cor- 

 puscles of 650 species of Vertebrata; including 3 Cyclostomata, 

 ii Elasmobranchii, 75 Pisces, 17 Amphibia, 38 Reptilia, 265 

 Aves, and 241 Mammalia. Perusal of his figures with a con- 

 sideration of the relative degree of activity of the various animals 

 indicates a general agreement with that to be expected if cell 

 size does vary inversely with activity, but there are numerous 

 exceptions. Most of these exceptions can be explained on the 

 basis of the size of the animal, for Gulliver points out that, within 

 a limited group, the size of the red blood corpuscles increases 

 with increasing weight of the members of the different species 

 considered. That activity may be of importance in connection 

 with cell size is indicated by the fact that, among the Mammalia, 

 the smallest corpuscles are found in the deer family, the largest 

 in the elephant, porpoise, anteater, and sloth and near the 

 average size among the Carnivora. Among the Cheiroptera the 



