EEFLEX ACTION OF THE SPINAL CORD. 411 



of excitement ; but the limbs are at once thrown into convulsions 

 by the slightest irritation applied to the skin, as, for example, the 

 contact of a hair or a feather, or even the jarring of the table on 

 which the animal is placed. That the convulsions in cases of 

 poisoning by strychnine are always of a reflex character, and never 

 spontaneous, is shown by the following fact first noticed by Ber- 

 nard, 1 viz., that if a frog be poisoned after division of the posterior 

 roots of all the spinal nerves, while the anterior roots are left un- 

 touched, death takes place as usual, but is not preceded by any con- 

 vulsions. In this instance the convulsions are absent simply 

 because, owing to the division of the posterior roots, external irri- 

 tations cannot be communicated to the cord. 



The reflex action, above described, may be seen very distinctly 

 in the human subject, in certain cases of disease of the spinal cord. 

 If the upper portion of the cord be disintegrated by inflammatory 

 softening, so that its middle and lower portions lose their natural 

 connection with the brain, paralysis of voluntary motion and loss of 

 sensation ensue in all parts of the body below the seat of the ana- 

 tomical lesion. Under these conditions, the patient is incapable of 

 making any muscular exertion in the paralyzed parts, and is uncon- 

 scious of any injury done to the integument in the same region. 

 Notwithstanding this, if the soles of the feet be gently irritated 

 with a feather, or with the point of a needle, a convulsive twitch- 

 ing of the toes will often take place, and even retractile movements 

 of the leg and thigh, altogether without the patient's knowledge. 

 Such movements may frequently be excited by simply allowing 

 the cool air to come suddenly in contact with the lower extremities. 

 We have repeatedly witnessed these phenomena, in a case of dis- 

 ease of the spinal cord, where the paralysis and insensibility of the 

 lower extremities were complete. Many other similar instances 

 are reported by various authors. 



The existence of this reflex action of the cord has enabled the 

 physiologist to ascertain several other important facts concerning 

 the mode of operation of the nervous system. M. Bernard has 

 demonstrated, 2 by a series of extremely ingenious experiments on 

 the action of poisonous substances, 1st, that the irritability of the 

 muscles may be destroyed, while that of the nerves remains unal- 



1 Lemons sur les effets des Substances toxiques et medicamenteuses, Paris, 1857, 

 p. 357. 



2 Ibid., Chaps. 23 and 24. 



