58 PHYSIOLOGY CHAP. 



or are, on the other hand, suppressed so that the effects of 

 deficiency can be studied. Few physiologists have attempted 

 to classify them according to rational criteria. Magendie seems 

 to have been the first who divided the internal sensations into 

 four groups, on a physiological basis : 



(a) The first come into play when it is desirable that the 

 organs should function. This group comprises the wants, desires, 

 and instinctive appetites that originate from a too protracted 

 abstinence. Such are hunger, thirst, desire to micturate or to 

 del'aecate, sexual desire, etc. 



(b) The second appear during the activity of the organs. They 

 are often obscure or quite subconscious sensations ; but may be 

 urgent, as the sensations felt during the excretion of urine or 

 faeces, and especially during ejaculation, which is the culminating 

 point of sexual activity. Highly important among the sensations 

 of this group, and one of the best studied, is that of tension, 

 constriction, and effort felt during muscular activity, by which we 

 judge of the range, speed, direction, and energy of our movements. 



(c) The third group includes the feelings that arise after 

 protracted or energetic action of the organs. Such is the sense 

 of fatigue that succeeds after too prolonged or excessive activity 

 of the muscles, drowsiness after long waking, the feeling of 

 exhaustion and languor after sexual indulgence, of satiety after 

 a full meal, etc. 



(d) The fourth group includes the innumerable internal sensa- 

 tions associated with illness, which range from a vague general 

 sense of discomfort to more or less acute and diffuse pain. In this 

 group we may include the shivering which ushers in attacks of 

 fever, the heaviness and burning in the head which is more or 

 less characteristic of febrile processes, the vertigo often present 

 in attacks of nervous illness, the nausea that precedes vomiting, 

 the so-called " visceral hallucinations," etc. 



However ingenious this classification may be it is incomplete. 

 It omits two other groups of bodily feelings, which are no less 

 important in their effects although vague and indefinite in 

 character, so that it is doubtful whether they normally cross the 

 threshold of consciousness. These are : 



(0) The common sensation of well-being or coenaesthesia con- 

 comitant with the state of perfect health, which is expressed 

 in adolescence by a more or less accentuated exuberance of 

 movement. 



(/) The obscure feeling by which we become aware of the 

 position of our body and its individual parts (head, trunk, limbs) ; 

 and the equally obscure sense of equilibration and orientation of 

 the body in respect of the external world, in so far as these can 

 be independent of the active state of the muscles and the specific 

 external senses. 



