July 24, 1896.] 



SCIENCE. 



97 



the sensory nerves shows us why this 

 should be the case, for these nerves are dis- 

 tributed only to points where under nor- 

 mal circumstances they can receive stimu- 

 lation, and thus serve to bring the organism 

 into relation with the outer world. Pain, 

 caused by excessive) stimulation of a sensory 

 nerve, is the sign that the integrity of the 

 body is threatened by some external agency, 

 and at this signal the body reacts con- 

 sciously or unconsciously to ward off the 

 threatened danger. Now external agencies 

 can act upon the body only at the surface. 

 Hence sensory nerves distributed to inter- 

 nal organs would have no raison d^etre ; 

 and, in the wise economy of nature, we 

 find, accordingly, that they do not exist. 

 The apparent contradiction to this state- 

 ment furnished by the painful sensations, 

 e. (J., cramps and colics which we sometimes 

 experience in our internal organs, are really 

 illustrations of the same general law, for 

 the pain in this case is the indication of 

 some morbid action of an organ, and is usu- 

 ally the sign that rest is necessary to en- 

 able the organ to recover its normal condi- 

 tion. It is a matter of common experience, 

 therefore, that the cutting of the skin is 

 the only really painful part of even quite 

 serious operations. As the knife divides 

 the deeper organs no pain is felt, except 

 indeed when a sensory nerve- trunk is di- 

 vided, which operation is attended by a 

 momentary flash of pain. Even the brain, 

 the seat of consciousness itself, is no ex- 

 ception to this rule, for its substance may 

 be cut and operated on in various ways 

 without causing the slightest pain. It is 

 evident, therefore, that in a large propor- 

 tion of the actually painful experiments 

 performed in physiological laboratories the 

 pain must be of the briefest duration, since 

 it is almost wholly confined to the prelimi- 

 nary incision . It must al so be borne in mind 

 that a large class of experiments consists 

 in the introduction of drugs under the skin, 



an operation about as painful as vaccina- 

 tion or as a subcutaneous injection of mor- 

 phia. Bearing these facts in mind we are 

 well prepared to accept Prof. Yeo's esti- 

 mate, that of the twenty-five per cent, 

 of actually painful experiments, twenty per 

 cent are about as painful as vaccination, 

 four per cent, about as painful as the heal- 

 ing of a wound, and one per cent, as pain- 

 ful as an ordinary surgical operation per- 

 formed without anaesthetics. 



I have thus sought to set before you the 

 material for forming a judgment with re- 

 gard to the amount of animal suffering 

 which the practice of experimental physiol- 

 ogy involves. It remains for me now to 

 speak of the value of the discoveries thus 

 made, or, in other words, to present to you 

 briefly the evidence of the debt owed by 

 the practising physician of the present day 

 to the physiologists of the past. We shall 

 then be in a position to answer the ques- 

 tion whether on the whole ' vivisection 

 pays.' To enumerate all the discoveries 

 that have been made in physiology by means 

 of experiments on animals would be utterly 

 impossible within the limits of this dis- 

 course, for there is hardly a single organ of 

 the human body whose functions have not 

 been investigated and explained in this 

 way. It will suffice at this time to call 

 your attention to a few of the more impor- 

 tant physiological discoveries which form 

 the groundwork of our knowledge of the 

 human body and to ask you to imagine, if 

 you can, what would be the condition of 

 the healing art if these discoveries had 

 never been made. 



To begin with, let us consider the circu- 

 lation of the blood, the discovery of which 

 bears somewhat the same relation to medi- 

 cine that that of the law of gravitation 

 bears to physics. It is well known that 

 the ancients believed the arteries, as their 

 name implies, to be tubes containing air. 

 When Galen, in the second century of our 



