iv.] ATROPHINE ; MERCURIC CHLORIDE 65 



seconds as the response becomes more sluggish. And this 

 has been a true physiological latency ; it is of the same order 

 as the similar effect that will be demonstrated to you on a 

 mammal, which a priori you might have expected to react 

 more quickly (infra, p. 105). With the capillary electrometer, 

 and excitation by a single strong induction shock, the latency 

 came out at 0.9 sec. 



40. In connection with the action of nerve upon skin, one 

 naturally thinks of atropin the drug which so promptly abolishes 

 the action of secreto-motor nerve and remembering how small 

 a dose of atropin dries the mouth and dries the skin in the case 

 of man, you have reason to anticipate that atropin, if it produces 

 an effect at all, will do so when it has been administered to the 

 animal by subcutaneous injection. I have not found this to be 

 the case in two experiments ; the nerves of atropinised frogs acted 

 perfectly well upon the skin, but after the drug had been applied 

 to the skin itself, the nerves ceased to be effective. So, in order 

 to demonstrate that atropin acts, it will be preferable to test it by 

 local application ; and to show this quickly, it will be best to apply 

 the drug to the external surface of the skin. 



A second nerve-skin preparation is set up, for an experiment 

 to consist of three steps. These will be : firstly, to see that indirect 

 excitation (from the nerve) is effective ; secondly, to apply atropin 

 to the skin, and see that the indirect effect is abolished, but that 

 an effect can still be produced by direct excitation ; finally, to 

 show that this direct effect is abolished by mercuric chloride. 



With indirect excitation you see that the large deflection before 

 application of atropin has been completely abolished by atropin. 

 The nerve no longer acts upon the skin. But the response to 

 direct excitation is quite well marked ; (and note in passing that 

 it is to your right in the positive or outgoing direction). I now 

 apply some mercuric chloride solution to the external surface, and 

 you see that direct excitation gives no response. The skin is dead. 



41. The effects of direct excitation deserve and will repay 

 closer study. The first and only allusion to these effects that I 

 am acquainted with, occurs in Engelmann's paper of 1872, sub- 



E 



