3 oo SCIENCE PROGRESS 



cavities of the brain with fluid — hydrocephalus, popularly 

 known as " water on the brain" — or there may be overgrowth 

 of the connective tissue causing arrest of development of the 

 nerve cells and fibres — the essential structures of mind. 



Microscopic Examination oj the Brain oj the Child before Birth 

 and after Birth, and What it Teaches. — There is no white matter 

 in the cerebral hemispheres before birth because the myelin 

 sheath of the nerve fibres has not been deposited around the 

 axial processes of the afferent, efferent, and association fibres 

 proceeding to and from the cortical grey matter. Appropriate 

 staining of thin sections of the brain shows no evidence of 

 myelin sheath formation. Now when the myelin sheath is 

 formed an indication is afforded that a particular system of 

 nerve fibres is capable of functioning by conducting nervous 

 impulses. We shall see that this important fact has been made 

 use of by Flechsig for showing certain fundamental principles 

 connected with the development and correlation of structure and 

 function in the growing infant's brain after birth. But before 

 proceeding to discuss this I will consider the structure of the 

 grey matter — the cortex — of the child's brain before birth. 

 Examined microscopically, we see that it consists of six layers 

 of cells, as the diagram of the adult brain shows, with indi- 

 vidual differences in different parts ; but these differences are not 

 so marked as in the adult brain. In fact, Brodmann has shown 

 from his studies of foetal brains that the six-layer type is the 

 characteristic type. 



We also observe that the cells are very simple in their form 

 and that they are closely packed together, forming columns and 

 layers. They increase in size and they grow and develop by 

 pushing out processes which extend like the branches of a tree 

 (fig. 2). There are two types of neurone : the first type, the larger, 

 in which a process of the cell called the axon leaves the grey 

 matter; it becomes covered with myelin and forms a nerve 

 fibre. In the other, the second type, the axon never leaves the 

 grey matter. It is probable that these two different types of 

 neurones have fundamental differences in function. The small 

 second type is especially numerous, forming a dense layer in 

 the sensory regions of the cortex of the brain. The sensory 

 projection system of fibres conveying nerve currents from the 

 muscles and special sense organs to the brain terminate in the 

 layer of small neurones. 



