CHAPTER X 



KNOWLEDGE is becoming more intimately connected with 

 daily life. We do not wish to store it in print for the 

 pleasure of seeing it grow, as the miser gloats over his 

 hoard. As knowledge grows, it becomes more and more 

 a guide for conduct ; with its help we predict events and 

 control them for our benefit, as much as possible. In 

 short, man's efforts to obtain knowledge appear as efforts 

 to obtain benefit. 



In this chapter I shall endeavour to point out the 

 bearing of the Mutation Theory in practical matters. 

 Other writers have pointed out its value to the breeder 

 of economic plants and domestic animals. We will not 

 pursue the subject in those directions. The Mutation 

 Theory has also a bearing on certain branches of pathology, 

 especially on mental and other congenital diseases and 

 on all those diseases that are due to parasitic organisms 

 of any kind. 



Many diseases may be described as one kind of 

 organism invading another. The manifestations of such 

 diseases, are a result of the interaction of two different 

 organisms both liable to vary. In the method of their 

 variation they must obey the unknown laws, which no 

 doubt govern variation among all living things. The 

 method of variation is essentially alike in the vertebrate 

 animals, the insect and the flowering plant, nor can we 



