The Problem of Adaptation 29 
living in the water might not be killed, which would be the 
case if the ice sank to the bottom, but such a method of 
interpreting physical phenomena would scarcely commend 
itself to a physicist. 
The formation of a covering of oxide over the surface of 
a piece of iron delays the further process of oxidation, but 
who will imagine that this property of iron has been ac- 
quired in order to prevent the iron from being destroyed by 
oxygen? 
If a piece is broken from a crystal, and the crystal is 
suspended in a saturated solution of the same substance, 
new material is deposited over its whole surface, and, as it 
grows larger, the broken side is completed and the crystal 
assumes its characteristic form. But of what advantage is 
it to the crystal whether it is complete or incomplete? In 
the case of an animal it is of some importance to be able 
to complete itself after injury, because it can then better 
obtain the food necessary to keep it alive, or it can better 
escape its enemies; but this is not the case with the crystal. 
In conclusion, therefore, it is obvious that the adaptations 
of organisms are something peculiar to living things, and 
their obvious purpose is to maintain the integrity of the indi- 
vidual, or that of the species to which the individual 
belongs. We are, therefore, confronted with the question 
as to how this peculiarity has come to be associated with 
the material out of which living things are made. In sub- 
sequent chapters this will be fully discussed, but before we 
take up this topic, it will be necessary to reach some under- 
standing in regard to the theory of evolution, for the whole 
subsequent issue will turn upon the question of the origin of 
the forms of animals and plants living at the present time. 
