CEREBRAL LOCALIZATION. 601 



Two methods of investigation are open to the physiologist the 

 experimental and the clinical. In the order of time, the first and the 

 most practicable is the experimental method, which consists in ob- 

 serving the brain through openings in the skull and exciting the con- 

 volutions or removing them according to the end proposed. This 

 method is applicable only to animals ; and the monkey, from the like- 

 ness of his brain to that of man, is best suited to these investigations. 

 But experiments upon other animals are very useful. They show the 

 homologous i-egions in different cerebral types ; and the inequality in 

 relative importance of the central masses, the region of automatic 

 functions, and the convolutions, the region of the will. The great 

 advantage of this method is that the operator can repeat the experi- 

 ments indefinitely upon all sorts of animals, varying the conditions, 

 and choosing his own time and place. Lesions can also be better cir- 

 cumscribed, and the autopsy can be made at will. On the other hand, 

 animals can not tell their sensations, and we have to judge as best we 

 can as to affections of the intellectual and sensational regions. And 

 the preliminary operations may cause general symptoms that mask the 

 phenomena to be studied. Still, this method is in merited favor, and 

 it will yet yield answers to many questions if we know how to put 

 them. 



All the processes of experimenters may be reduced to two catego- 

 ries, according to their effects upon the functional activity of the con- 

 volutions. These are irritating lesions and paralyzing lesions. Irri- 

 tating lesions provoke spasms when applied to the motor region, 

 subjective sensations when applied to the sensitive region, and delir- 

 ium when they affect the intellectual region. Paralyzing lesions in 

 the motor region paralyze the normal action, and in the sensitive and 

 intellectual regions bring on ansesthesia and mental depression. But 

 this division applies only to immediate results, for it is not rare to 

 see a lesion, whether experimental or in clinic, provoke symptoms of 

 irritation in the beginning, followed by paralytic symptoms, and re- 

 ciprocally. 



Experiments that produce prompt paralyzing effects are more nu- 

 merous than those which excite the functions of the convolutions. 

 But the most preferable one, and that adopted by Ferrier, is the 

 method of limited ablation. By it lesions can be more circumscribed, 

 it affords a sure means of control, and hence it has come largely 

 into use. Electricity is the only process for exciting the functions to 

 greater activity ; and since it has been much opposed, and is the sole 

 support of the theory of cerebral localization, we must defend its 

 legitimacy. 



It may be remarked that the convolutions of the brain are in the 

 form of long, round, gray swellings, separated by furrows. Each of 

 these swellings has a direction, relations, and a situation peculiar to 

 itself, and identical for all animals of the same species ; and the princi- 



