66 BIOLOGY 



influences exerted by their neighbours, either blood- 

 relations or not, and finally that most potent of all 

 vital agents, man. We may, therefore, look at the 

 organism as a minute living unit surrounded, as it were, 

 by an infinitely large barrel, whose staves are formed 

 of these influences, mechanical, chemical, physical, and 

 vital, arranged in an infinitely complex manner. These 

 influences may be looked upon as either helping or 

 hindering the organism in its healthy development. It 

 must be remembered, however, that these influences 

 seldom act singly, but always in some combination, 

 influencing the organism, it is true, but also interacting 

 among themselves and modifying each other in such a 

 way that the final result may be quite the opposite of 

 what was expected. 



We may now quote a few examples to illustrate the 

 chief effects of environment. It is quite impossible in 

 the space at our disposal to give anything like an ade- 

 quate idea of the various adaptations that exist, or to 

 recount in any way the numerous experiments that have 

 been carried out in this branch of Biology. 



It has been found by experiment that, when certain 

 animals are kept and bred in a confined space, the 

 offspring tend to diminish in size and ultimately a dwarf 

 race is produced. That this curtailment of space is an 

 important feature in nature itself, is proved by the fact 

 that rabbits, which were introduced into Porto Santo 

 in the fifteenth century, are now represented by a dwarf 

 race. An interesting point in connection with these 

 experiments is that these dwarfed forms are incapable of 

 interbreeding with normal forms of the same species, 



