86 ZOOLOGY. 



the constituent parts of animal bodies affects every struc- 

 ture and origin, and that an entire renewal of the body occurs 

 in every seven years. This opinion is not based on direct 

 experiment, and seems, indeed, contrary to the fact. Many 

 organs remain for long periods stationary, although it may be 

 admit ted that, under peculiar circumstances, the original tissues 

 themselves may be attacked, as after long fasting. Thus, 

 the curious experiments of M. Chossat show that when 

 birds do not find in their food a sufficient proportion of 

 caleareuiis matters, the phosphate of lime entering into the 

 composition of their bones is taken away, little by little. 



Now, the blood furnishing, as we have seen, the materials 

 of the various humours which the animal economy constantly 

 rejects and expels from it by the route of the secretions, 

 becomes unceasingly impoverished, and might take away 

 from the organs the soluble principles they contain, if the 

 repeated introduction of foreign substances did not maintain 

 this liquid always saturated with the same principles. It 

 results from this, that this introduction of the alimentary 

 matters into the organism is necessary, not only to effect the 

 increase of the living parts, but to secure the conservation or 

 preservation of the tissues already existing, and to prevent 

 the resorption or re-absorption of their constituent materials. 

 In brief, the nutrient matter introduced continually into the 

 blood is necessary, no doubt, not only for the growth of the 

 body, but also to maintain all the organs in their integrity, 

 and to prevent their being acted on by absorption. 



Finally, the slow combustion taking place in every part of 

 the body also destroys the combustible matters ; and unless 

 this destruction be met by constant renewal, it would seem, 

 from the experiments of Dumas and others, that the oxygen 

 would act on and destroy the materials composing the organs 

 themselves. From the aliments there must come the com- 

 bustible matters for the oxygen to act on, by means of which 

 they are transformed into carbonic acid gas and water, and in 

 that form eliminated from the body ; from the same source 

 are derived the materials of growth and of secretion. 



But whether the carbonated and hydrogenated matters 

 thus consumed come from the aliment directly or from the 

 tissues themselves, one thing is obvious, that the loss must 

 be supplied from without, under the form of aliments. 



The alimentary matters, which contain only carbon, hy- 

 drogen, and oxygen in their ultimate composition, such as 





