602 PHYSIOLOGY CHAP. 



hemiamblyopia of the side opposite to the injured hemisphere, 

 which were transient and only lasted from eight to twenty days. 



Imamura confirmed the observations of Luciani, Loeb, and 

 Hitzig, that when the visual disturbances due to removal of one 

 portion of the cortex have disappeared, they reappear in an 

 aggravated form and in both eyes after a second symmetrical 

 lesion of the other hemisphere. 



Lastly, in a final series of researches, Imamura also divided 

 the corpus callosum ; he confirmed Lo Monaco's observation that 

 this produces no appreciable effects in intact dogs, and he found 

 that if this operation is succeeded by unilateral extirpation of any 

 region of the convex surface of the brain, the usual visual disturb- 

 ances that follow show no tendency to disappear even within two 

 months. He further saw that if the corpus callosum is cut in 

 dogs in which the symptoms of cortical extirpation had been 

 compensated, the visual troubles reappear and persist. This 

 demonstrates the importance of the corpus callosum, as it contains 

 the paths through which compensation of the hemiamblyopia due 

 to unilateral lesions takes place. 



The experimental conclusions obtained from the dog are in 

 evident contradiction with those obtained experimentally from 

 the monkey, and particularly with the anatomical and clinical 

 observations of Hun, Henschen, Flechsig, and Niessl, on man, 

 which limit the visual sphere to the middle and lower surface of 

 the occipital lobe, precisely to the so-called calcarine area, in which, 

 according to the extensive histological researches of Brodrnann, 

 the cortex assumes a quite characteristic structure (zona striata 

 of Brodmann). 



A. Tschermak (1905) initiated a new series of researches, 

 intended to settle these differences and to determine the special 

 importance, in dogs as well, of the region homologous with the 

 calcarine area. 



On stimulating the medial posterior surface of the dog's brain, 

 and particularly the cortex lying round the sulcus recurrens 

 superior, which is homologous with the calcarine fissure of the 

 monkey and of man, Tschermak obtained co-ordinated movements 

 of the eyes; on excising the cortex of that area, he produced 

 hemianopsia and loss of the eye-reflexes on the opposite side. He 

 saw that these symptoms diminished, but did not entirely dis- 

 appear, even after a long period. Finally, he found descending 

 degeneration to the subcortical visual centres from the area 

 destroyed. Consequently in the dog the visual sphere is localised 

 to the medial surface of the hemispheres, in the region homologous 

 with the calcarine area. The parieto-occipital convexity may repre- 

 sent the association zone in the dog, as suggested by Flechsig. 



Fr. Kurzveil (1909), working under Tschermak's guidance, 

 confirmed his results, and stated that the alterations in vision and 



