122 THE NEW PHYSIOLOGY. 



wish to emphasise, however, is the great improbability, 

 on general grounds, of the hypothesis. The further 

 physiological knowledge advances, the more evident 

 does it become that each part and each activity of the 

 body is intimately dependent on the other parts and 

 activities. Life is a whole of which the elements cannot 

 be isolated without changing them. The whole is in 

 all the parts, including the environment. Now, Weis- 

 mann's hypothesis assumes that the germ-cells are no 

 more a part of this whole than if they were mere para- 

 sites. There is no warrant for such an assumption, 

 and every known relevant fact seems to me against it. 

 Just as the presence of the germ-cells, and their develop- 

 ment, influences the parent organism profoundly, so, 

 I think we must assume, do changes in the parent organ- 

 ism influence the germ-cells. They are part of that whole 

 which is in all the parts and their environments ; and, 

 if so, acquired characters must be capable of hereditary 

 transmission. 



It takes time, and often frequent repetition, to develop 

 adaptation. Otherwise the lesson is, as it were, forgotten, 

 and but little progress results. An adaptation which 

 may not remain fixed in even the tissues of the parent 

 organism can hardly be expected to be easily transmitted 

 to offspring ; but that there nevertheless is transmission 

 of adaptations which generation after generation of 

 parent organisms undergo, I can feel no doubt. The 

 adaptive response will thus become more and more easy 

 till at last it becomes established as a normal event in 

 individual development — in other words, a definite 

 race-adaptation. 



Weismann's theory of the physiological isolation of 



