THE BEGINNINGS OF LIFE. 33 



position to the doctrines of Liebig, that the heat which 

 is transformed into mechanical energy is by no means 

 necessarily derived from the combustion of nitroge- 

 nous substances , and, least of all, from an oxidation 

 of the substance of the muscle itself. This doctrine of 

 Liebig, which was for a long time accepted by many 

 physiologists, was from the commencement rejected by 

 a few, and notably so by Mayer, in his celebrated 

 memoir before alluded to 1 . In this memoir he insisted 

 that c A muscle is only an apparatus by means of 

 which the transformation of force is brought about, 

 but it is not the substance by the chemical change of 

 which the mechanical effect is produced/ The recent 

 admirable researches of MM. Fick and Wislicenus 2 

 are entirely in favour of this notion. They found, in 

 making a mountain ascent, that the total combustion 

 of nitrogenous materials would only suffice to produce 

 about one-half of the tota] effective energy which must 

 have been expended during the excursion. This and 

 other considerations render it almost certain that the 

 heat which is converted into mechanical energy during 



comme les taons peuvent suivre pendant de longues heures un cheval 

 lancd au grand trot. Par une belle jour-ne'e de mai ou de juin 1'abeille 

 vole d'une manifere continue du matin au soir, pour aller cueillir dans les 

 corolles des fleurs et rapporter k la ruche les materiaux necessaires aux 

 travaux et k la nourriture de la communautd.' 



1 ' Organic Movement in its Relation to Material Changes,' Heilbronn, 

 1845. 



2 ' Philosophical Magazine,' vol. xxxi. p. 485. For most important 

 additional facts and explanations, see a paper by Prof. Parkes in ' Pro- 

 ceedings of the Royal Society,' 1867, pp. 53-59. 



D 



