352 RECENT ADVANCES IN SCIENCE. 



heart. To all these discussions Weber's experiment came as a great 

 light in a dark place. 



There is no need for me to insist how this knowledge that impulses 

 descending the vagus slow or restrain the heart beat, and the knowl- 

 edge genetically dependent on this, that impulses reaching the heart 

 along the cardiac sympathetic nerves from the thoracic spinal cord stir 

 up the heart to more vigorous or frequent beats, have since served as a 

 guide for the physician in the intricate problems of cardiac disease, 

 and that with increasing security as our knowledge of the details of 

 the actions has increased. The knowledge may not always have been 

 wisely used. On this point perhaps I may be allowed to repeat the 

 caution which I may have given elsewhere concerning the dangers of 

 taking a new physiological fact direct and straight, raw and bleeding, 

 as it were, from the laboratory to the bedside. The wise physiologist 

 takes care, even in physiology itself, not to use a new fact as an expla- 

 nation of old problems without a due testing and a direct verification 

 of its applicability. How much more is it needful that the doctor who 

 sails not on the calm seas of the phenomena of health, but amid the 

 troubled tempests which we call disease, should not hastily and heed- 

 lessly rush to make practical use of a new fact, tempting as the use 

 may be, until he also has tested its applicability by that clinical study 

 which is his only sure guide. But this is by the way. 



In the second place, as a mere method Weber's discovery has in 

 physiological experimentation borne most important fruit. Before 

 Weber's experiment many an investigation, not only on the vascular 

 system itself, but in many other branches of physiology, came to a 

 standstill or went astray because the experimenter had not the means 

 on the one hand to stop or slacken, or on the other to quicken and stir 

 up the heart without interfering largely with the object of. his research. 

 Thanks to Weber's experiment and what has come out of it, that can 

 now be done with ease, and thus solutions have been obtained of prob- 

 lems which otherwise seemed insoluble. 



In the third place, the experiment has had a r^rofound and wide- 

 spread influence by serving to introduce a new idea, that idea which we 

 now denote by the word inhibition. Before the experiment, though 

 men's minds were gradually getting clearer concerning the nature of a 

 nervous impulse, all known instances of the action of a nervous impulse 

 had for the result an expenditure of energy; and it was a still open 

 though hotly debated question whether in such actions as when a muscle 

 was thrown into contraction by a nervous impulse this feature of expend- 

 iture was not impressed on the muscle by the very nature of the impulse 

 itself. That question the experiment answered in the negative once 

 and for all. Whatever the exact nature of a nervous impulse, it was 

 evidently of such a kind th-at it might on occasion check expenditure 

 and bank up energy in an increased potential store. Observation soon 

 showed that the heart and vagus was no solitary example. It was 



