Mabch 29, 1907] 



SCIENCE 



487 



normally contract on both sides simultane- 

 ously. The motor area of one side can 

 take charge of the muscles of both sides. 

 Such is the case with the motor areas of 

 the respiratory muscles, the muscles of the 

 larynx, of deglutition, etc. An injury to 

 the motor areas of these muscles in one 

 hemisphere only does not cause paralysis 

 of these muscles. An instance well known 

 to practitioners is the one-sided injury to 

 the motor area of the orbicularis palpe- 

 brarum. The muscle, as a rule, is not 

 paralyzed by such an injury, at least not 

 when the muscles on both sides contract 

 simultaneously. As is well known, the 

 absence or presence of paralysis of that 

 muscle in cases of facial paralysis serves 

 as a means to diagnose whether the paral- 

 ysis is of central or peripheral origin. 



An example of an uneconomical prin- 

 ciple, to use the expression of Verworn, 

 we find in the bilateral innervation of cer- 

 tain viscera by the pneumogastric nerves. 

 For instance, the normal rhythm of respi- 

 ration is completely changed when both 

 vagi are cut, whereas when only one vagus 

 is cut, the respiration remains normal. 

 Apparently one vagus nerve is amply suffi- 

 cient to carry on the regulation of respira- 

 tion. A similar condition obtains with 

 regard to the heart beats. For certain 

 animals, the dog for instance, the vagi 

 carry on an inhibitory tonus. When both 

 vagi are cut, the heart beats are consider- 

 ably increased in frequency; when only 

 one vagus is cut, the rate does not change. 

 Here again a single vagus nerve is suffi- 

 cient to carry on that inhibitory tonus. 

 Still more striking is the following fact. 

 After cutting both vagi, the animal dies 

 within a day or two from aspiration pneu- 

 monia, whereas when only one vagus is cut, 

 the animal not only survives the operation, 

 but is for all purposes apparently perfectly 

 normal. One vagus nerve then is amply 



sufficient to carry on all these functions; 

 but the body is provided with two nerves. 

 According to Verworn this should be an 

 example of a violation of the principle of 

 economy in the animal body and its exist- 

 ence should be denied a priori. 



Further examples of the ample provision 

 of the structures of the body with factors 

 of safety we meet also in the organs of the 

 body which are not built on the bilateral 

 plan, the unsymmetrical organs. We shall 

 mention here first the pancreas with re- 

 spect to its internal secretion. It is now 

 common knowledge that the complete re- 

 moval of the pancreas leads to glyctemia 

 and glycosuria. But here we note the fact 

 that if a small part of the gland, say not 

 more than one tenth, is left in the body, no 

 ill effects follow such an extirpation. One 

 tenth of that gland is capable of completely 

 protecting the animal against glycosuria; 

 but the body is, nevertheless, provided with 

 ten times as much. 



Another striking example is the liver. 

 This organ has many important functions. 

 It converts the sugar into glycogen ; it con- 

 verts the poisonous ammonia compounds 

 into the comparatively harmless urea. It 

 forms bile which carries out poisons from 

 the body, removes waste products, assists 

 in some way or another in the absorption 

 of fats, aids in the digestion of proteids 

 and what not more. But Ponfick found 

 that the removal of one half of that organ 

 practically does not interfere with the life 

 of the animal, and the successful removal 

 of even three fourths of the organ does not 

 produce symptoms indicating that any of 

 its functions are seriously interfered with. 

 That organ then is provided with an abun- 

 dance of active tissue considerably in ex- 

 cess of its normal requirements. 



Similar striking examples of factors of 

 safety we meet with in the luxurious con- 

 struction of the gastro-intestinal canal. 



