44 PSYCIIOLOOT. 



to have established this, although Muuk found that all his 

 animals were made totally blind.* 



In dogs also Munk found absolute stone-blindness after 

 ablation of the occipital lobes. He went farther and 

 mapped out determinate portions of the cortex thereupon, 

 which he considered correlated with definite segments of the 

 two retinae, so that destruction of given portions of the cor- 

 tex produces blindness of the retinal centre, top, bottom, 

 or right or left side, of the same or opposite eye. There 

 seems little doubt that this definite correlation is mythologi- 

 cal. Other observers, Hitzig, Goltz, Luciani, Loeb, Exner, 

 etc., find, whatever part of the cortex may be ablated on 

 one side, that there usually results a hemiopic disturbance 

 of both eyes, slight and transient when the anterior lobes 

 are the parts attacked, grave when an occipital lobe is the 

 seat of injury, and lasting in proportion to the latter's 

 extent. According to Loeb, the defect is a dimness of vis- 

 ion (' hemiamblyopia') in which (however severe) the centres 

 remain the best seeing portions of the retina, just as they 

 are in normal dogs. The lateral or temporal part of each 

 retina seems to be in exclusive connection with the cortex 

 of its own side. The centre and nasal part of each seems, 

 on the contrary, to be connected with the cortex of the 

 opposite hemispheres. Loeb, who takes broader views 

 than any one, conceives the hemiamblyopia as he con- 

 ceives the motor disturbances, namely, as the expression 

 of an increased inertia in the Avhole optical machinery, of 

 which the result is to make the animal respond with greater 

 efibrt to impressions coming from the half of space opposed 

 to the side of the lesion. If a dog has right hemiamblyopia, 

 say, and two pieces of meat are hung before him at once, 

 he invariably turns first to the one on his left. But if the 

 lesion be a slight one, shaking slightly the piece of meat 

 on his right (this makes of it a stronger stimulus) makes him 

 seize upon it first. If only one piece of meat be offered, he 

 takes it, on whichever side it be. 



When both occipital lobes are extensively destroyed 

 total blindness may result. Munk maps out his ' Seh- 



* A. Christiani: Zur PhA'siol. d. Gehirnes (Berlin, 1885), chaps, ii, iii, iv. 

 H. Munk : Berlin Akad. Stzgsb. 1884, xxiv. 



