This tendency toward specialization is a natural thing, and is quite in line with what has taken place in other fields of investigation.
When any science becomes an independent discipline, it is recognized that it is a more or less limited field in which work of a certain kind is done in a certain way.

Other fields and other kinds of work are to some extent ignored.

But it is quite to be expected that there should be some dispute, especially at first, as to what does or does not properly fall within the limits of a given science.

Where these limits shall be placed is, after all, a matter of convenience; and sometimes it is not well to be too strict in marking off one field from another.
It is well to watch the actual development of a science, and to note the direction instinctively taken by investigators in that particular field.
If we compare the psychology of a generation or so ago with that of the present day, we cannot but be struck with the fact that there is an increasing tendency to treat psychology as a _natural science_.

By this is not meant, of course, that there is no difference between psychology and the sciences that concern themselves with the world of material things--psychology has to do primarily with minds and not with bodies.