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SCIENCE. 



[N. S. Vol. IV. No. 82*- 



caused a human being exquisite agony. 

 It is evident, therefore, that it is entirely 

 impossible to draw conclusions with regard 

 to the sensations of animals by an effort to 

 imagine what our own would be under 

 similar circumstances. Our common hu- 

 man nature, which serves as a guide, though 

 an imperfect one, in estimating the suffer- 

 ings of other human beings, fails us entirely 

 when we have to do with animals, and we 

 are left to draw conclusions from cries, mo- 

 tions and other external signs of suffering. 

 Now these external signs are apt to be mis- 

 leading, for they only prove " that some- 

 thing is going on which the organism re- 

 pels," but do not prove that the animal is 

 conscious of what is going on. In other 

 words, the cries and struggles of an ani- 

 mal whose skin is cut or burnt belong to 

 that class of phenomena known as ' reflex 

 actions ; ' i. e., they are movements having 

 their origin in impressions made on the 

 terminations of the nerves, and not in im- 

 pulses coming from the nerve centers in 

 the brain. They may be accompanied by 

 consciousness, but consciousness, so far 

 from being necessary for their production, 

 acts rather to check and interfere with 

 their manifestation. 



We are all perfectly well aware that 

 when the spinal cord of an animal has been 

 divided in the cervical region, an impres- 

 sion made upon the nerves of the skin? 

 either by a sharp instrument or a chemical 

 irritant, will cause the animal to execute 

 violent movements of a very definite char- 

 acter, adapted to remove the source of 

 irritation and differing in no respect, ex- 

 cept, perhaps in increased energy, from 

 the movements of a perfectly uninjured 

 animal. But in this case we know that 

 the movements are not attended by con- 

 sciousness, for by division of the spinal cord 

 the channel by which impressions are con- 

 veyed to the nerve centers, whose activity 

 is a necessary condition of consciousness. 



is entirely obliterated. The movements 

 are, in fact, no more indicative of suffering 

 than are the convulsive flutterings of a de- 

 capitated chicken. We can speak with 

 great positiveness upon this point, for the 

 testimony of hospital patients suffering from 

 injuries to the spinal cord shows clearly that 

 violent reflex movements of the lower limbs 

 may occur absolutely unattended by con- 

 sciousness. It is, moreover, a matter of 

 common experience that in certain stages 

 anaesthesia consciousness may be entirely 

 abolished, while the activity of the lower 

 reflex centers remains unaffected. In such 

 cases patients may struggle and scream 

 during an operation, but subsequently de- 

 clare that they have suffered no pain. 



It is evident, therefore, that great caution 

 must be exercised in drawing conclusions 

 with regard to the sensations of animals 

 from the external signs of suffering which 

 they manifest when undergoing operations, 

 and that the ' spasm of agony ' of sensa- 

 tional writers is in most cases much better 

 described as a nerve-muscle reaction. 



We have thus seen that for the produc- 

 tion of a painful sensation three things are 

 necessary : 



First, the stimulation of a sensory nerve 

 or its terminations. 



Second, the transmission of the stimulus 

 to the nerve centers whose activity is as- 

 sociated with consciousness. 



Third, the response of these nerve centers 

 to the stimulus thus received. 



Pain may then be defined as the conscious- 

 ness, of the excessive stimulation of a sensory 

 nerve. This definition excludes those cases 

 in which the brain is narcotized or sepa- 

 rated from the rest of the nervous system, so 

 that there can be no consciousness of the 

 stimulation of the nerve, however severe it 

 may be, and also those cases where the 

 stimulation of the nerve is moderate in 

 amount and therefore gives rise to agree- 

 able sensations. The precise point where 



