2j8 Letter of Spallanxani to C. Senelier 



vigour, though the worms were reduced by long ebulhtiori 

 to such a state that their parts scarcely adhered. I sub- 

 jected to experiment by both these processes different kinds 

 of these animals, which compose the order of terrestrial and 

 aquatic testacea, and the result was always the same. Th» 

 singularity of this phenomenon made me seriously think 

 that there might be something equivocal in this absorption 

 of oxygen, and I almost conceived the possibility of it. 



In each of these analyses, not only the natural proportion 

 of the oxygen gas to the azotic gas was changed, but there 

 was always a certain quantity of carbonic acid gas. I then 

 thought that this gas might be the result of oxygen 

 comSined with the carbon of the animal. But in this case 

 it was evident that the, animals would not appropriate to 

 themselves the base of the oxygen gas which they dimi- 

 nished. My reasoning acquired strength by an observation 

 which taught me that when, instead of shutting up the ani- 

 mals in common air, I inclosed them in pure oxygen gas, 

 the quantity of that gas destroyed was more considerable ; 

 and the case was the same with that of the carbonic acid g^is 

 produced. 



This observation, however, did not appear to me decisive; 

 because it might have happened that the great quantity of 

 carbonic acid gas arose ti-om a greater affluence of carbonic 

 acid extracted from the animals by a greater quantity of 

 oxygen, which might excite in the animal fibre a strong mo- 

 tion, since it is proved that this substance has a very stimu- 

 lating force. 



The increase of the carbonic acid gas produced by ani- 

 mals placed in pure oxygen gas is not, indeed, constant, 

 since they several times consumed -^^^^ of this gas, while no 

 more than -jf^^ or -j-f;^ of carbonic acid gas was observed in 

 this atmosphere. In like manner, by making the experi- 

 ment with common air, one may see that when its oxygen 

 is entirely destroyed, it is not uncommon to discover in this 

 residuum only two or three hundredths of carbonic acid 

 gas. 



To clear up these apparent contradictions, I bad recourse 

 to an expedient which ought to be decisive : I placed dead 

 animals in a medium entirely deprived of ox)gen gas, be- 

 cause either no carbonic acid gas would be produced in that 

 gas, which v^ould have furnished me with an unanswerable 

 proof that the production of this gas depended on the oxy- 

 gen of the atmosphere; or, what is the same thing, that it 

 was the effect of the combination of this principle with the 



carbon 



