38o PRIMARY FACTORS OF ORGANIC EVOLUTION. 



may not flow from mechanical stresses applied in dif- 

 ferent ways. I suppose that any mechanical stress 

 which determines nutritive processes to a part, will in- 

 crease its size, ccrteris paribus ; and the stretch as well 

 as the impact has this effect. I have in fact shown, in 

 the observations already cited (pp. 277-279), on the 

 production of artificial elbow joints, that osseous de- 

 posit is stimulated by pulling strain as well as by push- 

 ing or impact. 



In concluding, Mr. Gary admits one of the two con- 

 tentions of the Neo-Lamarckians in his two closing 

 propositions. He says " Plasticity of bone, using the 

 word plasticity not in a physical sense merely, but to 

 include absorption under pressure, will probably ac- 

 count for much structure in the foot and elsewhere, 

 especially the connection with the joints, and in the 

 fields of variation and correlation." In the second 

 proposition he says that facts have been adduced by 

 him which are inconsistent with the theory that the 

 size of bones has been increased by the stimulus they 

 receive, and with the theory that regions of growth are 

 determined by regions of pressure and strain. "The 

 testimony of the literature as to the latter point," he 

 says, "is conflicting." I have shown that the supposed 

 conflict is due to a misunderstanding on the part of 

 the author of this paper. The proposition that pres- 

 sure doesViot affect growth is in contradiction to the 

 admission made by the author in his first proposition, 

 where he admits that pressure determines structure ; 

 for in such change of structure there is always growth. 

 Finally Mr. Gary remarks "That race changes follow 

 those produced in the individual life, or that they are 

 directly caused by their mechanical surroundings, I 

 do not think it has been satisfactorily shown." The 



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