ii SENSIBILITY OF THE INTEKNAL OKGANS 61 



most important modality of exaltation and perversion of the 

 sensibility of the internal organs and tissues is certainly repre- 

 sented by pain, in its various forms and varieties. 



In the last chapter we examined pain as one of the distinct 

 modalities of cutaneous sensibility, having nerves and nerve- 

 endings different from those of the other sense-organs of the skin. 

 But unlike the senses of pressure and of cold and heat, the sense 

 of pain is not specific, but belongs to the group of internal senses 

 that give rise to sensations that are incapable of transformation 

 into perceptions. It further differs from the other cutaneous 

 sensibilities in certain important characters ; it is not excited by 

 special adequate stimuli, but can be aroused by any kind of stimu- 

 lation (mechanical, thermal, electrical, chemical) that is capable 

 of acting on the nerve-fibres along their course ; it has incompar- 

 ably longer periods of latent excitation and after-excitation ; the 

 pain impulses have a greater capacity of summation so that the 

 sensation is rendered continuous'; and lastly, they have a greater 

 tendency to spread in every direction and have no precise local 

 signs, excepting the cutaneous pain spots which according to 

 Ponzo's recent work can be localised as exactly as the touch spots. 



The sensitiveness of the skin to pain is only a more evolved 

 and perfected form of the common sensibility proper to all 

 internal tissues that possess afferent nerves. This theory is by no 

 means new. The earliest physiologists distinguished pain, either 

 cutaneous or of the internal tissues and organs, from the specific 

 sensations, and referred it to the group of crude sensations 

 hunger, thirst, nausea, fatigue, etc. But, since on the ground of 

 v. Frey's work, the existence of special nerves and nerve-endings 

 for pain, constituting one of the cutaneous senses, is now admitted, 

 it must be asked whether these are capable only of reacting by 

 pain sensations to every kind of stimulus, or whether (like the 

 afferent nerves of the internal organs and tissues) they can also 

 react by obscure and non-painful sensations, i.e. can they transmit 

 subconscious sensations to the centres on normal weak stimulation, 

 and sensations of greater or less pain, which is more or less 

 conscious, on abnormal excessive stimulation ? All the evidence 

 is in favour of this last supposition. 



We have seen that pain is not a primordial form of sensibility, 

 but that, in the animal series, it develops along with the develop- 

 ment of intelligence, and is psychically superposed on the 

 protective subconscious reflexes, the better to protect the individual 

 from the injurious action of the outer world. As Foster pointed 

 out, " It may happen to a man to suffer pain in a particular region 

 or tissue of the body once only in the course of his life-time, or 

 possibly not even once; nay, we may suppose that in this or 

 that region or tissue pain is felt once only in one individual 

 among a large number of persons." In such a case, if there really 



