82 



Dr. R. Staehelin. On the Part played by [Dec. 11, 



In other experiments in which the frog was left longer exposed to 

 the action of benzene vapour, rigor mortis came on first in the hinder 

 and then in the fore extremities before the heart had ceased to beat. 

 One peculiarity was observed with regard to the reflex irritability of 

 the animals, under these conditions, which is worthy of notice. Very 

 early in the experiment, at the very beginning of the spasmodic move- 

 ments, the frog reacted very slightly and incompletely to changes in its 

 position, that is, such as would be produced by holding the vessel in 

 which they were placed in an oblique position or turning them on 

 their sides or backs. On the other hand, the reactions to tactile 

 stimuli of the skin were much more pronounced than usual, so that 

 & tap on the one foot might evoke muscular contractions throughout 

 the whole body. When the animals began to become rigid, stimula- 

 tion of a toe of the rigid limb could evoke contractions of the limbs 

 which had not yet become stiff. Thus, in all these experiments the 

 first result of the poisoning was motor excitation, which showed itself 

 at first by co-ordinated movements affecting large portions of the body, 

 and later by twitchings of isolated groups of muscles. A little later 

 the respiration became irregular and finally ceased. The higher 

 reflexes, e.g., the reaction to changes in position, were abolished, while 

 the lower were increased. Finally, however, the paralysis became 

 universal, so that also the spinal reflexes were abolished. This stage 

 was followed by a rigidity of the muscles, and last of all the heart 

 ceased to beat. The rapidity of onset of these phenomena is naturally 

 dependent on temperature, being quicker the higher the external 

 temperature. It is evident that we have, therefore, to deal with an 

 action of the poison on the central nervous system. The general 

 spasmodic movements are abolished by previous destruction of the 

 brain and spinal cord ; the twitchings of the muscles and the rigor of 

 the extremities persist, however, in the complete absence of the central 

 nervous system, and occur in a hind limb, the nerve of which has been 

 divided, as rapidly as on the opposite side. The onset is not pre- 

 vented by curarisation, and must, therefore, be ascribed to a direct 

 action of the benzene on the muscles themselves, as has been described 

 at the beginning of this paper. 



In the poisoning by coal gas this rigor of the muscles was not 

 observed either by myself or Vahlen and Kunkel, probably because 

 the animals die of asphyxia before the small amounts of benzene 

 present in the coal gas have time to bring about their direct effect 

 upon the muscular tissue. As Experiment I shows, the increase in 

 the percentage of benzene in the coal gas is followed by the onset of 

 rigidity in the muscles. 



Eather more difficult is the explanation of the increased reflex 

 excitability in the later stages of intoxication. It may be that the 

 poisonous effects are first confined to the higher centres. On the 



