J018 RESPIRATION, ANIMAL HEAT, DIGESTION. 



oxygen absorbed, the soluble matters in the blood are supposed 

 to be converted into lactic acid, an acid which has been observed 

 in the blood by Mitscherlich, Boutron-Chalard and Fremy. The 

 lactic acid itself becomes lactate of soda, and undergoing a true 

 combustion from combination with oxygen is converted into 

 carbonate of soda. The last salt is decomposed in its turn by 

 a new portion of lactic acid, and the carbonic acid set free, 

 with which the venous blood comes charged to the lungs. 

 The conversion of farinaceous matters into lactic acid, out of the 

 body, by the action of a special ferment, is a fact well under- 

 stood; and the discharge by the urine, of salts of the organic 

 acids, such as tartrates, acetates and citrates, in the form of 

 alkaline carbonates, has also long been observed. The large 

 production of lactic acid in the blood, and its conversion by 

 oxidation into carbonic acid may therefore be admitted. 



The oxidation occurring in respiration is quite sufficient to 

 account for the animal heat. MM. Dulong and Depretz 

 observed an excess of heat, in their experiments upon animals, 

 which was ascribed by them, and by physiologists generally, to 

 a .calorific power peculiar to the animal and independant of 

 respiration. But in these experiments it was assumed that an 

 animal placed in a calorimeter with cold water, leaves it having 

 exactly the temperature with which it entered ; a thing abso- 

 lutely impossible, as is now known. The cooling of the animal 

 occasioned the excess of heat obtained in their experiments. 



The animal frame appears thus to have eminently the cha- 

 racter of an apparatus of combustion, by which the complex 

 substances which are formed in the vegetable world and serve 

 as food to animals, are converted again into simpler forms of 

 matter, such as carbonic acid, water and other oxidated products, 

 which are returned to the atmosphere and to the soil to become 

 again the food of plants.* 



Digestion. The principal constituents of flesh and the animal 

 fluids are all azotised substances, namely fibrin, albumen and 



* " To mount to the summit of Mont-Blanc, a man requires two days of twelve 

 hours. During that time he burns on an average 300 grammes (10 ounces and 

 258 grains avoirdupois) of carbon or the equivalent of hydrogen. If a steam engine 

 were employed to carry him there, it would burn from 1COO to 1200 grammes, to 

 do the same work." Lcpon sur la Statiquc chimiquc dcs etres organises, professdc 

 par M. Dumas. 



