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SCIENCE 



[N. S. Vol. XXXVI. No. 922 



position through the instrumentality of an 

 electric current generated by a single nerve- 

 impulse whose electromotive force is not 

 greater than 0.015 of a volt. "We have not 

 rendered nerve impulses evident to sight, but 

 we have measured the electromotive force of 

 their electrical manifestations as accurately as 

 we measure the rise of temperature caused by 

 minute quantities of heat. 



We need not be surprised to be told that it 

 was universally believed that nerve-impulses 

 traveled with incalculable speed, that a flash 

 of thought and a flash of lightning were both 

 prodigiously rapid. In 1850 Professor Helm- 

 holtz measured the velocity of the nerve-im- 

 pulse, and ascertained it to be about 40 meters 

 a second in the nerves of man. Thus the 

 movements of the spirits, once thought so 

 erratic, have been measured; the intangible is 

 still intangible, but the immaterial has been 

 found to be in material and as such to be as 

 real as the material, neither more nor less so. 



Of late years there has been a very distinct 

 tendency towards concreteness in regard to 

 ideas of nerve-force and its diminution in 

 fatigue and in disease. At one time nerve- 

 force seemed to be the special property of the 

 quack and the charlatan, but the microscope 

 which has solved so many problems for us has 

 shed its light also on this most elusive subject. 

 A substance has been discovered in the interior 

 of nerve-cells which is found to accumulate as 

 the cell rests and to be worn away the longer 

 the cell has been active. The substance takes 

 the form of minute granules or prisms called 

 after their German discoverer the gTanules of 

 Nissl. The nerve-cells innervating the wing 

 muscles of a sparrow have been examined in 

 the early morning before the bird has begun 

 to fly about, and similar cells have been scru- 

 tinized in a wholly similar bird after a long 

 day of activity; on comparing these two sets 

 of cells under the microscope, the thing 

 wherein they were found to differ was the 

 quantity and appearance of the granules of 

 Nissl. Since these granules tend to disappear 

 when nerve cells are active, and to reconstitute 

 themselves when nerve cells rest, they are 

 evidently to be regarded as the physical basis 



of nerve energy, the local seat of the processes 

 concerned in the output and in the restoration 

 of nerve energy. 



It is clear, then, that the granules of Nissl 

 with the evolution of nerve energy and may be 

 called the dynamogenic material which is 

 widely distributed throughout the nervous sys- 

 tem. But it follows from this that fatigue, in 

 so far as it has a microscopical basis, will be 

 denoted by the more or less complete disin- 

 tegration of the granules. Fatigue, which as 

 understood by most people is merely a par- 

 ticular kind of feeling or sensation, has been 

 shown to produce a cognizable change in some 

 physical structure ; in other words, it has been 

 made concrete. General fatigue on its ob- 

 jective side has now been proved to be a con- 

 dition of bodily poisoning. The prolonged 

 activity of muscles and other tissues results in 

 the output of certain chemical materials 

 (fatigue-toxins) which, circulating in the 

 blood, produce a mild poisoning, one of the 

 effects of which is to depress the activity of 

 the cells of the central nervous system, the 

 objective sign of which is well knovni to be 

 the partial solution of the granules of Nissl. 

 Thus such comparatively indefinite and illu- 

 sive things as nerve force and fatigue have by 

 the microscopists and chemists of our time 

 been identified and shown to have a local 

 habitation and a general distribution respect- 

 ively in the minute recesses of the living ma- 

 terial of the body. The whole tendency here 

 has been towards the objectifying of the sub- 

 jective and the visibility of the unseen. 



But of course it is very largely in the sphere 

 of the healing art that this modern tendency 

 towards concreteness is Jo be seen in its high- 

 est perfection. Let us take the case of ma- 

 laria or ague, a disease the cause of which not 

 so very long ago was absolutely unknovra. 

 Not that it was not attributed to causes 

 such as " paludism," " telluric influences," ex- 

 halations, vapors, and so on, but these did not 

 explain anything. The word malaria is of 

 course derived from two Italian words mean- 

 ing " bad air " clearly showing that the at- 

 mosphere was held to be responsible for some 

 peculiar kind of corruption or infection as we 



