302 Journal of Comparative Neurology. 



eral visual power, and of the field of vision of forms and colors. 

 If there is a defect we exclude first meclianical disorders (of re- 

 fraction etc.), then affections of the retina and optic nerve ; 

 then we examine the reflex-irritability; if a scotoma was discov- 

 ered, especially for the area of the scotoma. This is of special 

 importance for the discrimination of certain forms of hemian- 

 opsia. Finally we search for subjective optic phenomena (from 

 the phosphemata to real hallucinations). Clinical and anatomical 

 pathology have furnished tables for localization and we dis- 

 tinguish the symptom complexes of: 



1. Mechanical lesions (optic disorders). 



2. Lesions of the retina. 



3. Lesions of the afferent optic neurones. 



4. Lesions of the cerebral afferent neurones. 



5. Lesions of intracortical or general character. — We 

 need not speak here of group i and 2. For group 5 are character- 

 istic : concentric constriction of field of vision and reversion of 

 the color-fields, and the more complex subjective phenomena 

 (hallucinations, fortification lines etc.). Lesions of group 3 and 

 4 are distinguished largely on anatomical grounds (presence or 

 absence and kind of hemianopsia), the involvement of the ' re- 

 flex-arc,' the appearance of the disks and especially accompa- 

 panying lesions of other mechanisms, as hemianaesthesia, 

 hemiplegia, mimic paralysis, etc. We must make here the 

 reservations necessary on account of the peculiar course of the 

 reflex path which is still under discussion (Redlich, Bechterew, 

 Massaut). 



Next would come hearing (mechanical, segmental af- 

 ferent or cerebral afferent lesions, or psychic condition ?), taste 

 (lesion limited to the segment of the 5th, 7th or 9th?) and fin- 

 ally the general sensibility. It would go altogether beyond the 

 domain of this essay to detail all these points. I have done as 

 much as I did in order to illustrate the method of correlation 

 of data of clinical and anatomical pathology, and merely add, 

 that for a diagnosis of ' sensory ' lesions we must know the do- 

 main of the branches of peripheral nerves, of the plexus, of 

 the nerve-roots and spinal and cranial segments, the hemian- 



