CHAP. IX.] THE CONTRACTILE TISSUES. 413 



in action and reaction between the vital organs and their respective 

 (habitual) stimuli, exactly in the sense of Girtanner. Irritability 

 co-exists with animal heat and keeps pace with it through life : 

 hence it probably has a similar origin. But, inasmuch as animal 

 heat can be shewn to be dependent upon vital air (oxygen), whose 

 latent heat, in short, is the source of the animal heat, may not vital 

 air be also the proximate cause of irritability I 



Beddoes a ^ ove v ^ ew was received with much favour, and 



therapeutical use was freely made of it. Dr Beddoes 

 discussed it in his Remarks on Girtanner s Essay, and is stated to have 

 specially pointed its reference to the case of muscle by the question, 

 Does muscular action or intumescence really depend upon the com- 

 bination of oxygen with hydrogen or azote (separately and combined in 

 various proportions) in consequence of a sort of explosion produced by 

 the nervous electricity 1 ? The advances which scientific theory makes 

 are often so insidious that we are apt to underrate their importance. 

 It is hardly too much to say that this question of Beddoes marks the 

 real point of departure of the modern views of muscular irritability. 

 Previously, the prevailing tone of thought had been semi-metaphysical. 

 Oxygen had been regarded as a principle, the presence of which 

 conferred irritability upon tissues, and the withdrawal of which from 

 the organs and fibres happened to be effected by its union with other 

 elements. Now attention was concentrated upon the union itself 

 rather than on the uniting bodies, and irritability was regarded as the 

 result of a process, and not the attribute of a substance. A taper, a 

 lamp, a fire, became the fashionable metaphors wherewith to illustrate 

 various physiological acts. Food was not useful food if it had no 

 affinity to oxygen. Life itself was but the burning of a lamp of which 

 the body is the wick and food the oil. 



Brandis Illustrations like these did not go uncriticised. "Such 



metaphors," remarked Brandis 2 , the German translator of 

 Darwin's Zoonomia, "are apt to cast shadows where we would fain have 

 light." It is indeed certain, argues this author, that phlogistic pro- 

 cesses occur in the body as in the combustion of other substances : 

 carbon is united to oxygen and expired as carbonic acid gas ; phos- 

 phorus appears to become acidified in the body and is excreted in the 

 urine in combination with lime ; and such probably is the case with 

 other constituents of the fibres. But there is as yet nothing to shew 

 that these bodies can excite themselves to union. Some external force 

 is needed to start the combustion, and to determine the intensity of it 

 in any particular act. This is the unknown and subtle vital force, 

 which is as indispensable to the vital processes as the spark is to the 

 kindling of a fire. 



1 Yeats, Op. ct., p. 171. Al. von Humboldt, Op- cit., Vol. n. p. 105. The original 

 Remarks seems to be somewhat rare, as neither Prof. Eudolf Heidenhain nor the author 

 has succeeded in obtaining a copy. 



2 J. D. Brandis, Versuch. ii. die Lebenskraft. Hannover, 1795. 



