804 THE AMERICAN JOURNAL OF SOCIOLOGY
most directly connected with social phenomena, we, as is assumed, meet with the constitutive factors of this notion of limits and boundaries which is the most simple and general expression of the differentiation of all bodies and their equilibrium.
First of all, our knowledge is limited ; memory depends upon the brain ; the latter has only a definite number, though enor- mous, of nervous elements, cells, and fibers ; thence the constant limitation, though relatively variable, of our acquisition. The gray matter which covers the cerebral hemispheres forms a sur- face, an inclosed field, of about nineteen square decimeters and an average thickness of two and a half millimeters ; this layer can contain about 1,200 million cells and 4,800 million fibers.
Each branch of knowledge, as mathematics, language, music, etc., is necessarily limited by the presence and coexistence of others ; despite their common lines, each cerebral localization is naturally limited by its neighbors. Locke, the founder of modern psychology, knew that first of all it was necessary to determine the limits of the human mind. He investigated the origin of our ideas and thus prepared the way for a natural history of their development. He applied the comparative method to this science, studying the intelligence of children and savages ; these studies were extended to animal intelligence. The way opened was good, and it finally led to the use of the experimental method from the time when the latter was used in physiology, thus mak- ing possible an exact science of psychology.
The material collected permits us now to affirm, with Huxley, that whatever may be the system of organs considered, the com- parative study of the modifications in the serial order of the primates leads to the conclusion that the anatomical differences separating man from the gorilla and the chimpanzee are smaller than the differences between the latter and the higher monkeys. From our observations of cerebral anatomy we can say that the primitive peoples are connected with the highest civilized peoples through intermediating varieties by imperceptible transitions, while between the most primitive peoples and the highest simian varieties the difference is enormous and abrupt, with a tendency to an increase of this difference either by the continuous disap-
