CHEMICAL IRRITANTS. 257 



is, as in all experiments by irritation, used for the pur- 

 pose, either in connection with the whole lower leg, or 

 only with the calf-muscle. If the effect of volatile 

 bodies vapours or gases is to be tested, the muscle 

 must be shut off from the nerve in an adequate manner. 



The muscle is extraordinarily sensitive to certain 

 substances. One part of hydrochloric acid in from one 

 thousand to two thousand parts of water affords strong 

 pulsations. The smallest trace of ammonia is enough 

 to cause strong contraction. The observer must there- 

 fore abstain from smoking whilst experimenting, for 

 the slight amount of ammonia in tobacco-smoke is suf- 

 ficient to elicit continued pulsations. The nerve, on 

 the contrary, is much less sensitive towards hydro- 

 chloric acid, and is not at all sensitive towards am- 

 monia. If the nerve is immersed in the strongest 

 solution of ammonia it very soon dies, but is not at 

 all irritated. These are the most marked differences. 

 But it must also be mentioned that glycerine and lactic 

 acid in concentration exercise an irritating effect on the 

 nerve, but not on the muscle ; and that when many 

 other substances (alkalies, salts) are applied, small dif- 

 ferences are exhibited, in that sometimes the nerves, 

 sometimes the muscles, contract in response to a some- 

 what thinner concentration. 



It thus appears that the differences are extremely 

 slight. Kiihne, however, attaches weight to these, and 

 interprets them as favourable to the theory of the in- 

 dependent irritability of muscle-substance. He sup- 

 ports this conclusion by the following observations. In 

 the case of specific muscle-irritants (ammonia, greatly 

 diluted hydrochloric acid) the result is the skme whether 

 the experiment is tried on an ordinary muscle, or on 



