INFLUENCE OF ENVIRONMENT 85 



the tissues of the new individual, acquire the special 

 properties of nerve-cells, muscle-cells, digestive- cells, 

 all the varied cells that compose the adult body, and 

 at the same time as they become specialized, lose the 

 general capacity to reproduce all the qualities of 

 the animal. The other portion may increase in size, 

 and may produce many daughter- cells, but these are 

 all alike, contain all the inherited qualities of the 

 organism, and form the sexual cells of the new genera- 

 tion. In such a fashion the germ-plasm, or hereditary 

 material of the stock, is handed on from generation 

 to generation. It lies passive in the tissues, pro- 

 tected and secluded from the changes and chances 

 that the environment may write on the body of 

 the individual containing it. Weismann's obser- 

 vations have been confirmed in the main, and it is 

 now generally accepted that the germ-plasm or 

 hereditary material, if not absolutely free from the 

 influences of the environment, has at least a very 

 high degree of stability, and hands on to the new 

 generation the characters of the generation from 

 which it came, with little contamination from the 

 effects of the environment on the organism in M-hich 

 it lies. Weismann's theory thus led to re-examination 

 of the belief in the inheritance of acquired characters, 

 and although opinion is far from unanimous, there 

 is general agreement that the inheritance of plastic 

 effects, of the moulding influence of the environ- 

 ment on the individual, is on the average extremely 

 slight. 



On the other hand, we are gaining an increased 

 knowledge of the power and effect of the environment 

 on each individual life. The resemblance between 



