INHIBITION AND CARDIAC VAGUS 125 



drops his tools on hearing the dinner-bell, it may be answered 

 that here we have a direct conditioned reflex over- 

 coming excitation which has been slackened in effect by 

 real exhaustion of energy. A true analogy for such 

 "inhibitions" as are seen in intestinal action, even 

 though little will be known of that until the Auerbach 

 and Meissner plexuses are fully understood, is a 

 labourer pausing, taking in oxygen, and gathering up 

 energy for a big task. For on stimulating the intestinal 

 vagus the graphs show a preliminary slowing, and then 

 ampler, more effective movements. 



That the inhibition theory is held firmly, even obstin- 

 ately, is no proof of its truth. Phlogiston was satisfactory 

 to many, and so apparently was "bad air" as a cause of 

 malaria. And yet Varro x in 36 B.C. actually attributed the 

 disease to minute animals. Columella even spoke of 

 mosquitoes as "armed with dangerous stings," animalia 

 infestis aculeis armata. It was necessary to wait nearly 

 two thousand years to get this verified by Ross and 

 Manson. It may be recollected that hundreds of years 

 ago an English physician was practically ruined by 

 attributing many diseases to invisibly small living agents. 

 Humoralists and solidists would be alike against him. 

 Von Uexkiill said that the object of science was not 

 truth but order, not having reached the pragmatic con- 

 ception that real order is truth ; but it does not seem 

 that the theories of inhibition have provided either. 



REFERENCES. 



Bayliss, W. M.— (i) "Principles of General Physiology," 1915 ; 

 (2) " Cardiac Vagus," Brit. Med. Journ., London, Sept. 28, 

 1918. 



1 See Appendix C, " Varro." 



