nave we Tu-o Brains? ly Dr. Brown- 



81 



or clearlv prove the conclusion ; and also when there ia 

 no fact that seems to be in opposition. It is requisite, 

 therefore, either that all the facts prove in favor of the 

 theory, or that together with a number in favor tlioro is 

 none at all in opposition. Such is not the case here. 

 There are a great many facts which show that a disease 

 in one halt' of the brain will produce complete loss of 

 sight of the two halves of one eye, either on the same 

 side or on the opposite side, or the two halves of both 

 eyes. Therefore there are three series of facts, and one 

 only would bo enough, which demonstrate that the 

 theory ought to be rejected. 



VISION AND THE HALVES OF THE BRAIN. 



But as regards sight wo find this, and it is a point of 

 fmportancb iu this lecture. Wo find that a disease any- 

 where in one-half of the brain can exist without any 

 alteration of sight at all. A disease existing in that 

 part where the optic nerve goes into the bruin, destroy- 

 ing that part altogether, may not bo a cause of loss of 

 sight; so that one optic tracu alone may be perfectly 

 sufficient for the functions of the two eyes. Therefore 

 I conclude that it is quite enough to have one brain to 

 Lave our power of sight; and as it is so for each half of 

 the brain, I can conclude and this is a point of import- 

 ance in this lecture I can conclude that each half 

 of the brain is independent of the other and each 

 of them possesses the powers of serving to the sensa- 

 tions of sight. You will ask how is it that a disease iu 

 certain cases in the brain will produce loss of sight, and 

 that a disease in the same part sometimes will not pro- 

 duce loss of sight. As regards that I cannot develop at 

 length what I would have to say, but if some of you 

 were present at my lecture in this city last year and 

 some of you present at the Academy of Sciences to-day 

 are here, they know that an alteration in any part of the 

 nervous system, whether in the brain or elsewhere, can, 

 by producing an irritation, act on other parts, so as to 

 produce the loss of a function of those other parts: 

 and so it is about sight particularly. In 

 many experiments I have ascertained that injuring 

 a small part of the spinal cord produces a loss of sight 

 in the eye on the same side. An injury to the medulla 

 oblongata a little higher than the part of the spinal cord 

 which produces loss of sight on the same side, will pro- 

 duce a loss of sight, but to the opposite eye. There is, 

 therefore, a power of producing by irritation a loss of 

 sight; and indeed there is nothing more common in chil 

 dren having worms in their bowels than a diminution 

 in the power of sight for a time, or some trouble in the 

 power of sight some change in the iris, some 

 change in the vessels of the eve, in fact 

 some disorder in the organs serving to vision. 

 Well, it is in the same way that an irritation existing in 

 certain parts of the brain will produce at a distance 

 from the place where it exists, a loss of the 

 function of sight. Tue cases that can serve 

 are, therefore, not those in which we find that the dis- 

 ease exists the loss of sight exists when there la a dis- 

 ease somewhere. The cases that can serve positively 

 must clearly bring us to a conclusion ; as those, on the 

 contrary, which establish that an injury in any part or 

 one-half of the brain aven in that part wlncli receives 

 the, optio track can exist without producing any loss 

 of sight; and that fact has been observed not very fre- 

 quently, but more than flve or six times to rny knowl- 

 edge and iu those cases in the most decisive manner. 

 Therefore the conclusion I have drawn is quite estab- 

 lished. Either half of the brain may serve to the power 

 of siglit. 



THE VOLUNTARY MOVKMKXTS. 



Now, as regards the volitional movemi -nts, the volun- 

 tary movements, if you ui;e. to call them so. Those 

 movements, as you well know, have been considered aa 

 depending on each half of the brain tor one-half of the 

 body. Still, many physiologists hive ascertained that 

 there are muscles iu our system in the nee];, in the eye, 

 in the throat, and in the back aNo-thero are, many 

 muscles which escape paralysis wlien Mien- is disease In 

 one-half of the brain; and for those parts at le.i.sl soaio 

 theory has been imagined to try to explain how it was 

 that the left half of the brain, for instance, is not the 

 regulator of the movements iu the right sides of the 

 body. I shall pass over that theory and come to the 

 point of importance in the object which I have in view. 



As regards volitional movements, tlc-ro are cases on 

 record which leave no doubt that either the anterior 

 lobe of the brain, the middle lobe of the brain, or the 

 posterior lobe, the throe essential parts of the organ, 

 can be destroyed and voluntary movements not be in- 

 terfered with at all; but still more, there are cases not 

 many, but a few Chat exist and are decisive. They 

 have been recorded by the most accurate observers, an 'I 

 some of them in hospitals whore there were many medi- 

 cal men and many students, so that there cannot be a 

 doubt about them. Tliere are many cases perhaps 

 the word "tnauv" is too strong, but there 

 are at least seven or eight to my knowl- 

 edgeof the destruction of the whole ha\f 

 of the brain without any interference with the voluntary 

 movement. Therefore we are not to look upon one-half 

 of the brain as being necessarily the organ serving to 

 the movement of the body on the opposite side. And 

 also another conclusion ; we are to look upon one-half of 

 the brain, in some individuals at least, as being able to 

 control voluntary movements in the two sides of the 

 body. If so, certainly the point I have in view that is, 

 that we have two brains is established as regards vol- 

 untary movements. We have certainly two brains as re- 

 gards voluntary movements; and if it is found in most 

 cases that even a slight injury limited to a small part of 

 the brain will produce a paralysis on the opposite side, 

 or sometimes on the corresponding side if that is 

 found, it is on account of this principle which I men- 

 tioned a moment ago ; that is, that an irritation iu any 

 part of the brain can affect functions iu other parts 

 through irritation. And I shall say about voluntary 

 movements what I have said about sight, and a worm in 

 the bowels, as well as an irritation in a tooth, or an irri- 

 tation in the ftomach. an irritation iu the lungs, an irri- 

 tation in the heart, an irritation in the skin; in other 

 words, an irritation wherever there is a nerve subject 

 to be irritated; an irritation there can produce 

 a paralysis as well as an irritation in a part of tlie bruin. 

 And therefore when we see a slight alteration m a very 

 limited part of the brain cause a complete paralysis on 

 the opposite side of the body, wo are not to conclude 

 that It is owing to the loss of function of voluntary 

 power there where the disease exists iu that small part, 

 but tli.it it depends or it has been Drought on by an ir- 

 ritation starting from the place wliero wo see the dis- 

 ease, and acting upou remote parts so as to produce the 

 loss of the function. The mere fact, I may say, that a 

 di.seasa exceedingly limited in extent can produce a 

 coinploto paralysis iu the opposte side of the 

 body, is sufficient to show that it docs not depend on tho 

 loss of the f unctiou of will ; for one-half of the body 

 cannot locate In a very limited part of the brain the 

 whole power of the will located in that bruin. If it 



