ACTION OF THE SPINAL CORD AS A NERVE-CENTRE. 



687 



tion, such as a breath of air or a slight jar, throws the entire muscular system into a 

 condition of violent tetanic spasm. The same phenomena are observed in cases of poison- 

 ing by strychnine or of tetanus in the human subject. This fact is important in its rela- 

 tions to the treatment of these conditions ; for it is evident that, 

 in such cases, the exhaustion due to the violent spasms may be 

 moderated by carefully avoiding all unnecessary irritation of 

 the surface. 



It was shown a number pf years ago, that the inhalation 

 of anaesthetic agents may abolish all of the ordinary reflex phe- 

 nomena. Whether this be due to an action upon the cord itself 

 or to a paralysis of the sensory nerves, it is difficult to determine. 

 Ordinarily, in animals rendered insensible by anaesthetics, the 

 movements of respiration continue ; but these also may be 

 arrested, as has been observed by all who have experimented 

 with anaesthetics, especially with chloroform. A common way 

 of determining that an animal is completely under the influence 

 of an annesthetic is by an absence of the reflex act of closing 

 the eyelids when the cornea is touched. 



It now only remains to show that the phenomena of reflex 

 action observed in experiments upon the inferior animals, espe- 

 cially frogs, are applicable to the human subject, and to indi- 

 cate the muscular actions which depend upon the cord as a 

 nerve-centre. 



It is only necessary, after what has gone before, to indicate 

 in a general way the phenomena observed in the human sub- 

 ject which illustrate the reflex action of the cord. It is a 

 common observation, in cases of paraplegia in which the lower 

 portion of the cord is intact, that movements of the limbs fol- 

 low titillation of the soles of the feet, these movements taking 

 place independently of the consciousness or the will ot the subject 

 experimented upon. Acephalous foetuses will present general 

 reflex movements and movements of respiration, and will even 

 suck when the finger is introduced into the mouth. Observations 

 FIG. 224. Frog poisoned with of this kind are so numerous and familiar that they need not be 

 cited in detail. Experiments have also been made upon crimi- 

 nals after decapitation ; and, although the reflex phenomena are not so well marked and 

 cannot be excited so long after death as in cold-blooded animals, they are sufficiently distinct. 

 It is difficult, in studying, in the human subject, the ordinary phenomena of move- 

 ments in the voluntary muscular system, to isolate the reflex phenomena from those acts 

 involving sensation and volition. In many persons, titillation of the soles of the feet pro- 

 duces violent contractions of muscles, which cannot be arrested by an effort of the will, and 

 this may even be followed by general convulsions. When we unexpectedly touch an irri- 

 tating surface with the hand, the muscles of the arm act so quickly that we may suppose 

 that this takes place before we really appreciate the painful sensation, and, if the impres- 

 sion be very severe, we may have movements more or less general ; in operating upon 

 highly-sensitive parts, it is frequently impossible to arrest reflex movements, as the closing 

 of the eyelids when the cornea is touched ; true reflex movements may be produced by 

 carefully-executed experiments upon persons asleep ; we cannot arrest the act of vomit- 

 ing induced by titillation of the fauces ; and other instances of this kind might be cited. 



Most of the true involuntary movements are reflex ; but these have been or will be 

 considered under their proper heads. The movements of deglutition depend upon an 

 impression made upon the mucous membrane of the pharynx, etc. The ejaculation of 

 semen is also reflex, although it may be produced without titillation of the genital orpin*, 

 as in emissions occurring during sleep. Important reflex actions take place through the 



