A HISTORY OF SCIENCE 



Schiff, who was hard upon the same track at the time 

 of Bernard's discovery. But a clear light was not 

 thrown on the subject until Bernard's experiments were 

 made in 1851. The experiments were soon after con- 

 firmed and extended by Brown-S6quard, Waller, 

 Budge, and numerous others, and henceforth physi- 

 ologists felt that they understood how the blood-supply 

 of any given part is regulated by the nervous system. 

 In reality, however, they had learned only half the 

 story, as Bernard himself proved only a few years later 

 by opening up a new and quite unsuspected chapter. 

 While experimenting in 1858 he discovered that there 

 are certain nerves supplying the heart which, if stimu- 

 lated, cause that organ to relax and cease beating. 

 As the heart is essentially nothing more than an ag- 

 gregation of muscles, this phenomenon was utterly 

 puzzling and without precedent in the experience of 

 physiologists. An impulse travelling along a motor 

 nerve had been supposed to be able to cause a muscular 

 contraction and to do nothing else; yet here such an 

 impulse had exactly the opposite effect. The only 

 tenable explanation seemed to be that this particular 

 impulse must arrest or inhibit the action of the im- 

 pulses that ordinarily cause the heart muscles to con- 

 tract. But the idea of such inhibition of one impulse 

 by another was utterly novel and at first difficult to 

 comprehend. Gradually, however, the idea took its 

 place in the current knowledge of nerve physiology, 

 and in time it came to be understood that what hap- 

 pens in the case of the heart nerve-supply is only a 

 particular case under a very general, indeed universal, 

 form of nervous action. Growing out of Bernard's 



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