CHAP. IX.] THE CONTRACTILE TISSUES. 415 



disintegration and union with oxygen. But if a portion of the vital 

 energy is diverted for the purposes of contraction, the natural incli- 

 nation of the muscle to change is, in part, unchecked, and a certain 

 portion of the tissue becomes oxidized and dead. For every motion 

 of contraction there is a material exchange, with an absorption of oxy- 

 gen, and a certain amount of tissue cast off. The relationship among 

 these is invariable : for every portion of force expended in motion 

 there is a definite proportion of tissue wasted and oxygen absorbed. 



Besides attacking living tissues which are for the moment left 

 unprotected by the vital force, the oxygen which is absorbed into the 

 body attacks those also which are already lifeless ; whence arises the 

 heat and the proper temperature of the body which is so important a 

 condition of vitality. The production of heat and force in the body 

 are indeed closely related; but heat can be produced without any 

 change in the living elements of the body, while mechanical effect 

 is always proportional to the amount of living matter which loses the 

 condition of life. However closely the conditions of this twofold 

 production seem to be connected in regard to mechanical effects, 

 yet the disengagement of heat can in no way be considered as in 

 itself the cause of these effects. All experience proves that there is in 

 the organism but one source of mechanical power, the conversion 

 of living into lifeless compounds. 



Thus for every portion of oxygen taken into the body there is 

 a corresponding proportion of heat and mechanical force produced. 

 Further, the amount of tissue metamorphosed in a given time is 

 measured by the nitrogen in the urine; and the sum of the mechanical 

 effects produced in each of two individuals at the same temperature, 

 is proportional to the nitrogen excreted by each. 



The views of Liebig were not left unchallenged. 

 J. R Mayer 1 , the early apostle of the conservation of 

 energy, in his treatise on organic movement in relation to material 

 exchange, exposed the inconsistencies of the doctrine of vital force as 

 expounded by Liebig, and stated that not only the heat, as Liebig 

 admitted, but also the muscular motions, of animals had but one 

 source in the oxidation of combustible matters. He calculated from 

 the combustion- heat of carbon, that the extraordinary consumption of 

 combustibles by a labouring animal, bearing in mind the enlarged 

 production of heat during labour, is fully competent to account in 

 a natural way for the work done. But the combustions in which the 

 animal movements take their origin are not combustions of the 

 substance of muscle itself. To account for the production of motion 

 in this way, we should have to assume a rapid destruction and 

 restoration of muscular tissue, of which there are no sufficient histo- 

 logical and physiological signs. The oxidations take place rather 

 in the blood, which is the true oil for the flame of life. 



1 J. E. Mayer, Die organische Bewegung in ihrem Zusammenhang mit dem Stqft'~ 

 wechsel. Ein Beitrag zur Naturkunde. Heilbronn, 1845. 



