960 



SCIENCE 



[N. S. Vol. XXXVII. No. 965 



in the former group of organisms. In its 

 most familiar aspect the complete organism, 

 e. g., a man, or an isolated living tissue, as 

 a nerve or muscle, fails during anesthesia 

 to show any response to a stimulus which 

 normally excites it strongly. In other 

 words, the capability of responding to stim- 

 uli — what we call "irritability" — is in 

 anesthesia diminished or lost. When the 

 condition passes off the normal responsive- 

 ness returns unimpaired. Thus a muscle 

 exposed to ether vapor soon ceases to con- 

 tract on stimulation ; under the same con- 

 ditions a nerve ceases to conduct ; in motile 

 plants like sensitive plants the characteris- 

 tic osmotic motor mechanisms cease to act. 

 Automatic activities like ameboid move- 

 ment, ciliary movement, protoplasmic flow- 

 ing, cell division, and growth may also be 

 brought temporarily to a rest by anesthet- 

 ics. Claude Bernard showed long ago that 

 seedlings ceased growth in an ether-impreg- 

 nated atmosphere, and resumed it when the 

 ether was removed. Fertilized egg-cells 

 cease to divide in the presence of an anes- 

 thetic in appropriate concentration, al- 

 though they remain living and proceed with 

 cell-division and development when the an- 

 esthetic is removed. Other less evident cell- 

 processes, including metabolism, are simi- 

 larly affected; the rate of oxidation is 

 usually slowed during anesthesia, though 

 there are. exceptions to this rule. 



It should be remembered that such de- 

 crease of the vital activity or responsiveness 

 is not a solely artificial phenomenon. Con- 

 ditions physiologically resembling anes- 

 thesia occur normally in the life of many 

 organisms ; sleep is in fact a kind of physio- 

 logical regularly recurring narcosis due ap- 

 parently to accumulation of certain meta- 

 bolic products in the blood or tissues. 

 Again, all irritable tissues lose their re- 

 sponsiveness for a brief period following 

 excitation ; this is the so-called ' ' refractory 



period," which has been compared with 

 narcosis by some physiologists. The re- 

 semblance in this case is probably superfi- 

 cial; but I call attention to this phenome- 

 non in order to show once more that tempo- 

 rary loss of irritability may occur under 

 normal or physiological conditions as well 

 as under artificial. There are also note- 

 worthy resemblances between narcosis and 

 fatigue. Thus the degree of irritability of 

 a tissue may vary within a wide range 

 under normal as well as artificial condi- 

 tions. 



We shall first inquire under what gen- 

 eral conditions irritable tissues undergo re- 

 versible decrease or loss of irritability. 

 These conditions are various. One of them 

 is cold. The living system operates within 

 a narrow range of temperature. Most irri- 

 table tissues or cells become less responsive 

 or lose irritability as the temperature ap- 

 proaches zero. In a muscle or nerve of a 

 cold-blooded animal the ability to respond 

 to stimulation is not necessarily decreased 

 by a moderate reduction of temperature — 

 in fact, slight cooling may increase the irri- 

 tability of nerve ; the tissue responds in the 

 typical manner, but the rate of the response 

 — as indicated by the duration of the single 

 contraction in muscle or of tlie electrical 

 variation in nerve — is always decreased, 

 typically to a degree corresponding to the 

 usual temperature-coefficient of chemical 

 reaction-velocity. In the neighborhood of 

 zero stronger stimuli becomes necessary to 

 elicit a response, and eventually none may 

 appear. Different organisms vary in these 

 respects. In some animals, as tropical 

 medusa?, irritability is abolished or greatly 

 lowered at a temperature considerably 

 above zero. The same is trae of warm- 

 blooded animals. On return to normal tem- 

 perature irritability is restored. 



Another condition producing effects re- 

 sembling anesthesia is lack of oxygen. This 



