CHAP. VL] THE BRAIN. 617 



one on which it does not as yet seem possible to make a dogmatic 

 statement. 



We compared the condition of a pigeon after injury to the 

 semi-circular canals to that of a person who is dizzy, and indeed 

 one great characteristic of vertigo or dizziness is an inability on the 

 part of the subject to maintain a due equilibrium ; he cannot co- 

 ordinate his movements properly or adapt them to the circum- 

 stances around him, and in consequence staggers and reels. Vertigo 

 may be brought about in various ways. It may be the result 

 simply of unusual and powerful visual sensations, such as those 

 produced by water falling rapidly from a great height or by objects 

 moving swiftly across the field of vision. It may arise from 

 changes taking place in the brain itself, and is a common symptom of 

 many maladies and of the action of many poisons. As is well known, 

 a most severe vertigo may be at once produced by rapidly rotating 

 the body ; and a very curious form may be induced by passing an 

 electric constant current of adequate strength through the head 

 from ear to ear. All cases of vertigo, however produced, have this 

 common subjective feature, that one or more of the sets of sensa- 

 tions which form the basis of our appreciation of the relation of our 

 body to external things disagree, and are in conflict with, the rest 

 of the sensations which go to make up the same appreciation. 

 Thus in the vertigo after rapid rotation of the body, while we seem 

 to see the whole world whirling round us, this conclusion is contra- 

 dicted by other sensations. Corresponding to this subjective feature 

 of vertigo is the objective feature of the failure of motor coordina- 

 tion ; and there can be no doubt that the two are connected 

 together as cause and effect. The exact manner in which the 

 vertigo is developed, i.e. the sequence and relation of the various 

 factors of it, will naturally vary according to the nature of the 

 exciting cause, and the course of events appears to be not only 

 different in different forms, but in many cases complex. When 

 vertigo comes on from rapidly rotating the body with the eyes 

 open, an element of discord is introduced by the eye-balls not 

 keeping pace with the movements of the head but following ir- 

 regularly, executing the oscillatory movements known as nystagmus, 

 movements which continue after the body has come to rest, and 

 then give rise to the false sensation that external objects are 

 moving rapidly. But in this vertigo of rotation there are other 

 factors at work, for the dizziness comes on, though less readily, 

 when the eyes are kept shut all the time. It has been suggested 

 that false ampullar sensations arise from the rotation of the body 

 exciting the semi-circular canals ; and the form of vertigo^ which is 

 the salient symptom of the so-called Meniere's malady, has been 

 ascribed to disease of the semi-circular canals. But it must be re- 

 membered that the canals are frequently diseased without any 

 vertigo appearing; and if, as some observers state, vertigo by rotation 

 may be readily induced in rabbits after section of both auditory 



