464 BIOLOGY. [BOOK vn. 



had pretended. All the aliments, all the organic substances become 

 oxydised while furnishing energy. This last proposition has been 

 put beyond doubt by MM. Fick and Wislicenus in their celebrated 

 ascent of the Faulhorn. 1 



These observers, after having previously ascertained the weight 

 of their bodies, and having subjected themselves during thirty- 

 six hours to a non azotised alimentation, ascended the Faulhorn, 

 taking care to ascertain the current of the urea expulsed during 

 the ascent, and the amount during the six hours following. 



Knowing their weight, and the height of the mountain above 

 the Lake of Brienz, they had the sum of the kilogrammetres, of 

 the units of labour. The weight of the excreted urea gave, ac- 

 cording to the figures of Frankland, the heat develope'd by the 

 combustion of the albuminoidal substances, and especially of the 

 muscular tissue. Now, the two experimentalists found that the 

 oxydation of azotised matters could not have supplied, at the 

 maximum, more than the half of the exterior labour accom- 

 plished, without taking into account frictions, the contractions 

 of the heart, thoracic movements, &c. 



Furthermore, Dr. Yerloren has remarked that many insects 

 feed specially upon albuminoidal matters at the time when they 

 accomplish little muscular labour, and, on the contrary, have an 

 alimentation almost exclusively ternary and non-azotised when 

 they labour much. He remarked also that bees and butterflies 

 feed upon substances very slightly azotised. 



The preceding facts permit us then to arrive at a proper 

 appreciation of the office and value of the diverse categories of 

 alimentary substances. 



1 Philosophical Magazine, t. XXXI. 



NOTE. 



It is not easy to express in English the distinction between forces vives and 

 forces vivantes. To lessen, not to vanquish, the difficulty the word vival his 

 been employed. Now and then in the translation of this work, French words 

 or expressions have, modified or unmodified, been from necessity used. 

 TRANSLATOR. 



