268 Mr. H. G. Seeley on the Origin 



muscle-substance, and by the covering of the bones dialyzing 

 osseous substance. Therefore fundamental! j the constitution of 

 the body into its anatomical machinery is a matter of chemistry. 

 And on the condition of the blood which supplies the material 

 to be dialyzed, and upon the condition of the dialyzing mem- 

 branes, depend changes which take place in the chemical com- 

 position of organic substances. Thus, under certain conditions, 

 the dialyzing function gets disordered ; and then, instead of the 

 body being maintained in healthy equilibrium, pseudomorphs 

 of muscles and bones are produced in other substances, com- 

 monly in fat. 



Under some circumstances the removal of substances from 

 the body is less rapid than their accumulation ; and this pro- 

 duces normal healthy increased growth, which, whether it 

 affect a special muscle or bone or the entire organism, is 

 spoken of as hypertrophy. Under other circumstances the 

 supply of material is less rapid than its removal, and results 

 in a diminution of growi;h, which is spoken of as atrophy. 

 Now, as the organic degeneration becomes faster or slower, 

 both relatively and actually, than the reconstruction, and vice 

 versa, so must all the parts of the body undergo changes in 

 their forms and sizes, which will constitute animals with an 

 infinite variety of shape and stature. But the result of a de- 

 fective quantity of nutriment is in some cases a smaller tissue, 

 while in other cases the tissue elaborated is of defective qua- 

 lity ; and there is as yet no known reason why one of these 

 conditions should prevail rather than the other. If the tissue 

 accumulated is of defective quality, it is probably fat, and in 

 some cases may be bone. On the other hand, the result of 

 superabundant nutriment is in some cases increase and im- 

 provement in the quality of the several fibres or particles, and 

 in other cases a multiplication of them ; that is, in hyper- 

 trophy some parts simply grow large, while in other cases new 

 parts are differentiated. And if hypertrophy and atrophy 

 operate together in the same individual, the result maybe that 

 in one organ a new part will be produced, while in another 

 organ an old part will be removed. Thus these natural pro- 

 cesses vary not only the shape and aspect of animals, but their 

 structures also. 



Hence it follows that the law of nutrition which produces 

 in different individuals of a human family visible difference of 

 form and function, is the same in kind, and only differs in 

 degree from the differentiation which constitutes separate spe- 

 cies and genera. In other words, if the hypertrophies and 

 atrophies of individuals could determinate towards special 

 parts, they would inevitably accumulate in the pliable young 



