60 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



shows irregular contractions, as the different fibres of the nerve are one after 

 the other affected. I f the (Irving has not been continued too long, the normal 

 irritability may be restored by supplying water. Muscles behave like nerves 

 in these respects. 



Most drugs and chemicals capable of altering the irritability of nerves and 

 muscles first increase and later destroy the irritability. If the change in the 

 chemical constitution of the nerve is sufficiently rapid, it maybe accompanied 

 by the phenomena of excitation. For example, veratria, eserin, digitalis, 

 most mineral acids, and many organic acids, free alkalies, most salts of heavy 

 metals, destroy the irritability of nerves and muscles, as a rule after first pro- 

 ducing increased excitability. Potash salts, if concentrated, rapidly kill, but 

 excite less than soda compounds. Verworn says : Acids, alkalies, and salts 

 have a similar effect on the protoplasm of a thick pseudopod of one of the 

 rhizopods of the Red Sea; they first excite and later paralyze, acting like 

 narcotics on the central nervous system. 



Ammonia, carbon disulphide, and ethereal oils may destroy the irritability 

 of nerves without causing excitations, at least not in sufficient amount to 

 produce visible muscular contractions. If applied directly to the muscle, 

 however, these substances excite contractions. 



The attempt to ascertain some exact relation between the molecular 

 weight of different salts and acids and their destructive power has encoun- 

 tered too many exceptions for the establishment of any definite rule ; in 

 general, however, the higher the molecular weight the stronger the effect on 

 the muscle. 1 Many gases and vapors have a marked effect on the irri- 

 tability and activity of protoplasm. 2 Carbonic-acid gas, tobacco-smoke, the 

 fumes of ether, alcohol, and chloroform, applied directly to exposed nerves, 

 first stimulate, later anaesthetize, and finally kill. C0 2 has a very powerful 

 effect, even a fiftieth of a milligram sufficing to influence profoundly the 

 activitv of the protoplasm of the nerve, a fact of considerable importance if 

 we recall that this gas is produced by the normal oxidation of carbon within 

 the tissues of the body. Tobacco-smoke acts like CO, and probably because 

 of the CO., which it contains. Alcohol first excites and then paralyzes the 

 nerve. If the fumes of alcohol have not acted for too long a time, the para- 

 lyzed nerve may recover its function, and the same is true for ether and 

 chloroform. These vapors, if present in considerable quantities act rapidly 

 upon exposed nerves; thus ether (diethyl oxide) will anesthetize a nerve in 

 three minutes ; if the drug be then removed, the nerve can completely recover 

 in five minutes. Chloroform would appear to be a more dangerous anaes- 

 thetic than ether, as recovery of the nerve is less likely to occur in case the 

 anaesthetic action is somewhat prolonged. Many other gases and fumes 

 chemically irritate and kill nerve-muscle protoplasm. 



From all these results it becomes evident that the normal irritability of 



»Blumenthal : Pjluger'a Arehiv, 1896, Bd. 62, S. 513. 



5 Waller: Lectures on Physiology, first series, " On Animal Electricity," London, 1897, pp. 

 42-46. 



