

SENSORY GANGLIA. CONSENSUAL ACTIONS. 707 



Birds and Mammals, may survive for many weeks or months (if their physical 

 wants be duly supplied) after the removal of the entire Cerebrum. It is diffi- 

 cult to substantiate the existence in them of actual sensation ; but some of 

 their movements appear to be of a higher kind than those resulting from mere 

 excito-motor action. One of the most remarkable phenomena exhibited by such 

 a being is the power of maintaining its equilibrium, which could scarcely exist 

 without consciousness. If it be laid upon the back, it rises again ; if pushed, 

 it walks. If a Bird thus mutilated be thrown into the air, it flies ; if a Frog 

 be touched, it leaps. It swallows food and liquid, when they are placed in its 

 mouth; and the digestive operations, the acts of excretion, &c., take place as 

 usual. In the case of a Pigeon experimented on by Malacorps, which is recorded 

 by Magendie, there appears sufficient proof of the persistence of a certain 

 amount of sensation. Although the animal was not affected by a strong light 

 suddenly made to fall upon its eyes, it was accustomed, when confined in a dark- 

 ened or partially illuminated room, to seek out the light parts ; and it avoided 

 objects that lay in its way. In the same manner, it did not seem to be affected 

 by sudden noises ; but at night, when it slept, with closed eyes and its head 

 under its wing, it would raise its head in a remarkable manner, and open its 

 eyes, on the slightest noise; speedily relapsing into a state of complete uncon- 

 sciousness. Its principal occupation was to prune its feathers and scratch it- 

 self. And Longet mentions that a Pigeon from which he had removed the en- 

 tire Cerebrum gave many indications of consciousness of light; not only the 

 pupil contracting, but the lids closing, when a strong light was suddenly made 

 to fall upon the eye, the animal having been previously kept in darkness ; and 

 when a lighted candle was made to move in a circle before it, the animal executed 

 a corresponding movement with its head. 1 The condition of such beings seems 

 to resemble that of a Man, who is in a slumber sufficiently deep to lose all 

 distinct perception of external objects, but who is yet conscious of sensations, as 

 appears from the movements occasioned by light or by sounds, or from those 

 which he executes to withdraw the body from an uneasy position ( 787). 



735. The results of other Experiments made upon the Sensory ganglia them- 

 selves, and upon the organs from which they derive their impressions, confirm 

 this view ; by showing that the ordinary movements are seriously perturbed, and 

 that in some instances a new set of automatic movements is induced, when the 

 ordinary relations between the sensory and motor apparatus are disarranged. 

 Among the ganglia of special sensation, the functions of the Optic Lobes, or 

 Corpora Quadrigemina, have been chiefly examined experimentally. The re- 

 searches of Flourens and Hertwig have shown that their connection with the 

 visual function, which might be inferred from their anatomical relations, is thus 

 substantiated. The partial loss of the ganglion on one side produces partial 

 loss of power and temporary blindness on the opposite side of the body, without 

 necessarily destroying the mobility of the pupil ; but the removal of a larger 

 portion or complete extirpation of it, occasions permanent blindness and immo- 

 bility of the pupil, with temporary muscular weakness on the opposite side. 

 This temporary disorder of the muscular system sometimes manifests itself (as 

 already stated) in a tendency to move on the axis, as if the animal were giddy. 

 No disturbance of consciousness appears to be produced ; and Hertwig states 

 that he never witnessed the convulsions which Flourens mentions as a conse- 

 quence of the operation, and which were probably occasioned by his incision 

 having been carried too deeply. As Longet has justly remarked, it is difficult, 



i It must not be forgotten that, in such experiments, the severity of the operation will 

 of itself occasion a suspension or disturbance of the functions of parts that remain ; so 

 that the loss of a power must not be at once inferred from the absence of its manifesta- 

 tions. But the persistence of a power, after the removal of a particular organ, is a clear 

 proof that it cannot be the peculiar attribute of that organ. 



