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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



side the key, a touch upon which will establish 

 the current, and on the other the needle which 

 will indicate the return of the current ; but the 

 two instruments are not directly connected to- 

 gether. The circuit, passing through a distant 

 place inaccessible to our observer, is formed by a 

 connected system of instruments influencing each 

 other, but each different from the others. The 

 first, we may say, is a bar, which the current pro- 

 duced will at once magnetize. This in its turn 

 sets a new instrument going, which a little farther 

 on causes the hand of a clock to advance ; and we 

 may thus continue indefinitely : the hand passing 

 over a point on the dial-plate, instantly establishes 

 a new current, which gives turning motion to the 

 mirror of a galvanometer, such as is used in the 

 transatlantic telegraphs; the luminous ray may 

 be so thrown on a mixture of gases as to make it 

 explode, and the explosion will give rise to a new 

 current, which comes again at last into the room 

 where we left the observer, and deflects the needle 

 under his eyes. He thus sees the current he sent out 

 come back to him ; he is conscious of the initial 

 act of pressure on the key ; he notes the final act 

 in seeing the deflection of the needle — but that is 

 all. He is ignorant alike of the number and the 

 nature of the transformations the current has 

 undergone in all those instruments, unknown to 

 him even by name ; and if it chances that the 

 transmission from one extremity of the circuit 

 to the other is completed ill or imperfectly, when 

 asked to explain the failure, he will by no possi- 

 bility be able to answer. The case of this ob- 

 server is a little like ours in presence of the cer- 

 ebral acts which separate volition from the regu- 

 ular performance of motion. We are conscious 

 of the initial act ; we see the ultimate phenome- 

 non, but all which separates them is utterly un- 

 known to us, and we have nothing to do with 

 discussing it. It is futile to seek to explain what 

 takes place in an apparatus which fulfills func- 

 tions for which as yet we have not even a name. 

 The ascertainment of the fact that the con- 

 nected sequence of nervous action takes place by 

 means of conductors, which unite the different 

 parts of the brain with each other, was enough to 

 suggest the thought that intellectual differences 

 in individuals may depend on the more or less 

 numerous combinations of the cerebral network. 

 The first idea was that of referring intelligence 

 to the volume of the brain. That of Cuvier, 

 which was found to be of extraordinary weight, 

 was often cited as an instance. That opinion 

 could not be maintained, and was necessarily 

 given up ; other instances, quite as famous and 



convincing, being found to discredit it. The 

 number and the complex plan of the superficial 

 convolutions of the organ were cited in turn as 

 unsuccessful. A professor of Munich collected 

 in the little physiological museum of the univer- 

 sity the exact casts of brains of a large number 

 of persons whose biography was well known. 

 They are professors or people of the city toler- 

 ably conspicuous during their lives. In showing 

 us his collection, he exhibited the one of all his 

 casts most remarkable for the abundance and the 

 fine marking of its convolutions ; doubtless the 

 brain of some dean or some eminent professor ? 

 It was the brain of a cobbler, well known at the 

 Munich University, but best known for the high 

 rates he charged for half- soling the students' 

 heavy jack-boots ! 



Though the weight or the coarser external con- 

 figuration of the brain teaches us nothing, it would 

 doubtless be otherwise with the inner structure. 

 Unfortunately, it is almost impossible to estimate, 

 even with the microscope, the differences it pre- 

 sents in different persons : for instance, the rela- 

 tive number of nerve-cells, the completeness or 

 imperfection of their mutual relations, the direc- 

 tion of their connecting fibres. And yet, spite 

 of our incapacity to distinguish in this way the 

 brain of a genius from that of a fool, the idea of 

 some difference of this kind is that which is most 

 strongly brought out by all our positive knowl- 

 edge of the nervous system ; and this, too, wheth- 

 er we follow ancient philosophy in regarding the 

 brain as an instrument of greater or less excel- 

 lence employed by an intellect equal in all per- 

 sons ; or whether, with biologists, we consider 

 the mind to be more or less perfect in proportion 

 to the perfection of its organ. However that 

 may be, without siding with either opinion, it 

 will be admitted, at any rate, that the regular 

 working of the mental faculties must clearly 

 depend chiefly on the reciprocal distribution of 

 the parts, cells, or tubes, that make up the brain ; 

 though many other causes, temporary in their in- 

 fluence, may intervene. If the current of the 

 blood becomes checked, ceasing to moisten the 

 nerve-matter, the intellect at once falls into a 

 swoon, like death ; and if, on the contrary, the 

 blood comes charged with certain principles 

 called intoxicating, such as hasheesh, opium, al- 

 cohol, belladonna, and many others, these sub- 

 stances, changing the chemical constitution of the 

 nerve-matter by their presence, disturb its func- 

 tions for a time. The least pressure on the gray 

 matter has as quick an effect in producing faint- 

 ing ; even idiocy itself has, perhaps, only a mere 



