ON THE CAUSES OF TURNING AND ROLLING. 713 



opposite to the punctured side of the medulla. A rabbit, which lived thirteen 

 days after the operation, had still the circulatory movement a few hours before 

 dying j although sometimes the animal could walk nearly straight for a few 

 seconds. 



3. Turning produced by a Puncture or a Section of the Acoustic Nerve. 

 Flourens has discovered that, after the section of the semicircular canals, 

 turning sometimes takes place. 



The author has found all the facts detailed in relation to this subject. It 

 was interesting to know if a puncture or the section of the auditive nerve would 

 produce turning. As it was impossible to operate on that nerve in mammals, 

 he experimented on frogs. In these amphibia, it is easy to find the nerve and 

 to act upon it. He found that, after a puncture or a section on the trunk of 

 the nerve, the animal begins instantly to turn. As long as the frogs live, after 

 a puncture of the acoustic nerve, they turn; but the circle of turning is much 

 smaller a short time after the operation than afterwards. He has kept such 

 frogs alive for months. 



4. On a New Mode of Turning. The same experimenter has discovered a 

 mode of turning which has some of the characters of both turning and rolling. 



In the circulatory movement called turning (mouvement de manege}, the body 

 of the animal is bent on one of the lateral sides. It has the shape of an arch, 

 and this arch is generally a part of the circumference described by the animal 

 when turning. The smaller the radius of that arch, the smaller is the circle of 

 turning. 



In the new mode of turning, the body of the animal is not bent, and when it 

 walks it moves laterally, instead of going forwards. In turning, it describes a 

 circle, but the longitudinal axis of its body, instead of being then a part of the 

 circumference, is a part of a radius, so that its head is at the circumference, and 

 its tail towards the centre of the described circle. 



This mode of turning has been performed by animals on whom the quadrigemi- 

 nal tubercles and the pons Varolii, on one side, had been punctured by a pin. 

 One of the eyes was convulsed ; the other was in its normal condition. The 

 convulsed eye was the right one, and the tubercles punctured were those of the 

 left side. 



5. On the Causes of Turning and Rolling. 1. As the slightest puncture of 

 certain parts of the encephalon is sufficient to produce turning or rolling, it is 

 evident that those rotating movements do not exist in consequence of an hemi- 

 plegia, as Lafargue, Longet, and Schiff believe they do. Another reason is that 

 every degree of hemiplegia exists in man without being accompanied by turning 

 or rolling. Besides, these phenomena have been observed in persons who had 

 no paralysis at all. 



2. The theories of Magendie and Flourens are also opposed by the fact that 

 a slight puncture is sufficient to produce turning or rolling. 



3. As to the theory of Henle, which is based upon the existence of convul- 

 sions in the eye, producing a kind of vertigo, it has against it the facts that, on 

 one side, convulsions may exist in the eyes without any other disorder in the 

 movements ; and, on the other side, sometimes turning or rolling exists without 

 any convulsion in the eyes. 1 



Nevertheless, in many cases, the vertigo consequent on convulsions of the 

 eyes is one element of the cause of turning. And in certain cases, paralysis 

 of some parts of the body may facilitate the rotatory movements. But their 

 great cause is the existence of a convulsive contraction in some of the muscles, 



1 [See a very remarkable case observed by Dr. Lebret, in "Comptes Rendus et Me- 

 moires de la Soc. Biologic," annee 1850, Paris, 1851, t. ii. p. 7.] 



