BIOLOGICAL SCIENCE 67 



physical defects which in former ages would have 

 destroyed their owner, and with him ceased from 

 troubling the human race, are now sometimes per- 

 petuated in his offspring, whose existence has been 

 made possible by this same improvement in the con- 

 ditions of life. If the innate qualities of our race 

 are to improve in the future as they have done in 

 the past, if indeed the race is to be preserved from 

 decay, such problems will have to be faced. 



We must now consider briefly the relations between 

 physics and chemistry on the one hand and the 

 biological sciences on the other. 



The bodies of plants and animals are clearly 

 subject to the usual laws of mechanics. As wholes 

 they fall with the usual acceleration of gravity; 

 their limbs illustrate the mechanical principles of 

 the lever. The breathing of animals is analogous 

 chemically to the burning of a candle, and organic 

 bodies are composed of the same chemical elements 

 that are familiar in the inorganic world. 



Nevertheless, carbon, which must be regarded as 

 the chief and most characteristic element in organic 

 matter, possesses properties more complicated than 

 those of other elements. A carbon atom is able to 

 combine with other carbon atoms, as well as with 

 those of different substances, to form very complex 

 molecules, and it is this property which makes pos- 

 sible the special chemistry of living processes. 



