1899.] on Structure of the Brain in Relation to its Functions. 129 



from the muscles and the surface of the body are received and rise 

 into consciousness. It was found by Fritsch and Hitzig that this 

 portion of the brain is excitable by electrical stimulation, and they 

 were able to map out in the dog the whole excitable surface of the 

 brain into definite areas, each area when electrically excited causing 

 a definite representative movement. Subsequently, Ferrier showed 

 the same in the monkey, which being nearer to man made the experi- 

 ments of greater value. This discovery was of the greatest import- 

 ance to the physiologist, physician and surgeon. It explained what 

 Hughlings Jackson had previously observed and described, namely, 

 the march of a fit due to local disease of this region of the brain. 

 He had observed that from a definite focus of irritation the spread of 

 the excitation as shown by the succession of definite movements tliat 

 occur in this form of epilepsy always began in the same way, and 

 gave rise to a definite series of movements of the same order and 

 character. If you look at the diagram you will understand how a fit 

 starting from irritation in the arm area will spread to the face area 

 below, and to the leg area above, causing convulsive movements in 

 the muscles. You will observe that other areas of the brain have 

 also been investigated, and we now know that the posterior part of 

 the brain, especially the inner surface, is connected with sight, 

 another with hearing, and another with taste and smell (Figs. 4 

 and 5). In the dog the sense of smell is highly developed, and is 

 the main avenue of intellectual experiences, and the incitement to 

 volitional action ; therefore the area of this sense in its brain is 

 highly developed. In man, on the contrary, the senses of smell and 

 taste, which stand like sentinels to guard the respiratory and 

 alimentary systems, are little connected with intellectual faculties, 

 and therefore not much developed. There is, however, yet a large 

 portion of the brain, quite two-thirds in fact, to which I have 

 allocated no special function. 



Flechsig, by studying the development of the structures of the 

 brain of the new born child and of infants of various ages, has shown 

 that certain parts of the brain are prepared for functional activity 

 before others. I will call your attention to the diagram Fig. 6, which 

 represents a slice through the brain of a child at birth ; only certain 

 definite systems of fibres are insulated by a myelin sheath, and 

 therefore ready to conduct nervous currents. For only those fibres 

 which have a sheath of myelin are stained purple by his method, 

 and thin slices of the brain can thus be made to reveal the 

 parts which are prepared for conduction. These are all tracts of 

 fibres which convey sensory impressions from the eye, skin, muscles, 

 ears, nose and mouth to the very portions of the brain which I have 

 already indicated to you that experiment and pathological observa- 

 tions have shown to be connected with the special sense functions. 

 These sensory tracts developed first then, are the primary avenues of 

 consciousness and of all the higher functions of the mind. All the 



Vol. XVI. (No. 93.) k 



