670 PHYSIOLOGY OF THE CEREBRUM 



describe them. They can also acquire new optical images, but it is much more 

 difficult than formerly. Sometimes the memory for old and familiar objects 

 as well as for less familiar ones is affected and the person cannot describe well- 

 known buildings and streets of his own town so as to direct another person 

 how to go from one point to another. In severe forms of mind blindness all 

 objects and persons alike appear strange, and may not be recognized even in 

 their general relations. 



What the patient is unable to recognize by optical impressions alone, he 

 can, however, properly orient by means of other impressions for example, audi- 

 tory impressions. Thus a patient who fails to recognize his own friends by 

 sight may recognize them by their voices, etc. 



Mind blindness comes on if the lesion extends to the white matter of the 

 occipital lobe, and in all probability is caused by the interruption of the asso- 

 ciation pathways and by injury to the association areas. It is not referable 

 to any definite locality, but can be produced by abscesses in different parts of 

 the lobe. In the great majority of cases thus far observed, the abscesses are 

 situated in both hemispheres. Mind blindness has not yet been observed as 

 the result of disease on the right side alone. 



The phenomena of mind blindness undoubtedly show that the occipital lobes 

 play a determining part in the proper evaluation of optical impressions. Ob- 

 servations on more extensive lesions of the posterior association center, in 

 Flechsig's sense, teach us also that mental disorders of a more serious nature 

 may result from the loss of its function. 



The first symptom of a diseased condition involving a large part of this 

 center is incoherence of ideas, that is, a primary intellectual deficiency and 

 something quite independent of the effects which follow purely and simply 

 as the result of a loss of ordinary associative connection of external impres- 

 sions. Many of these patients exhibit no lack of clearness as to their own 

 person, evince no lack of composure in their conduct, no deep perversion of 

 their feelings or desires; but they do not correctly interpret external objects, 

 and consequently misuse them. They mistake one person for another, and lose 

 their bearings both spatially and temporally. The mental images of what goes 

 on outside are lost, consequently a clear understanding of the external world 

 and that knowledge of it which is capable of being put into words; in short, 

 all empirical interpretations of external impressions are reduced to naught. 

 The patient has thus become impoverished for ideas, eventually nothing either 

 true or false enters his head he has become an idiot. 



D. FINAL SURVEY 



It is likely that in the more complicated mental processes all the associa- 

 tion and sensory centers cooperate, since they are united with each other by 

 numerous nerve fibers, and that from this cooperation results the harmony 

 of the cerebral functions. 



Flechsig has worked out some views with regard to the mechanics of the 

 higher brain functions, which I shall abstract briefly here, because among 

 modern researches on the brain which have a physiological bearing those of 

 Flechsig undoubtedly take first rank. 



