CHAPTER VI, 



The Causation of Structure — The Two Great Causes of Structure : 

 Heredity and Environment. 



The second aspect under which we must study the Causation, 

 of Disease is that of structure ; and this word, be it remem- 

 bered, refers not only to the grouping of individual cells, 

 into tissues, but also to the individual structure of the cells, 

 themselves. 



Upon what does structure depend ? What, in other words,, 

 are the factors which determine the particular structure of any 

 individual ? This is the problem which now confronts us — 

 this the question we must now answer, would we gain a philo- 

 sophical insight into the Causation of Disease ; for disease 

 being a two-sided process, of which the one side is structure 

 and the other environment, it follows that whatever affects 

 structure may play a part in its production. 



If we fix the mind on any one individual, disregarding for 

 the time those subtle agencies which, during the long past, 

 have moulded man into his present shape, we shall find the 

 great determining factor to be " Heredity " — this word con- 

 veniently summing up an inconceivably complex assemblage of 

 forces. The structure of any given individual depends chiefly, 

 in fact, upon the structure of his more immediate progenitors. 

 Compared with this great controlling influence, any other is 

 small and insignificant. If an elephant could give birth to a 

 cow, a bird to a fish, or a human being to a cat — if, in fact, 

 the principle of Heredity were fickle and irregular — we should 

 assign to it a minor part in shaping structure ; but inasmuch 

 as each of the many species of plant and animal gives origin 

 to an offspring like to itself, it is evident that heredity is 

 the great power which determines the particular structure of 



