264 Letter of Spallanzdni to C. Seneller 



animals have of absorbing oxygen in the air, is retained by 

 them in the water, though not destined to live in it, and 

 though it be fatal to them. 



Hitherto I have spoken of the organ of the skin, and 

 shown in the six classes of animals, that it has the power of 

 appropriating to itself the oxygen of the air, not only when 

 these animals are alive, but even after they are dead, I wish 

 to call your attention for a moment to this power commu- 

 nicated by nature to other parts, which, though essential to 

 their oeconomy, present themselves to the air as if they were 

 only accessary. I here allude to the shells of the terrestrial 

 and aquatic testacea : they belong, as you know, to the: 

 family of worms. 



When I observed that these dead animals decomposed 

 common air by absorbing its oxygen, I imagined that the 

 shells might contribute to this operation; because I consi- 

 dered that thev were organized according to the demonstra- 

 tion of Herissant, and that they formed a whole with the 

 •inimal which inhabited them. It was easy to verify this 

 idea by inclosingthe shells alone in conmionair, and the ef- 

 fect showed that my conjecture was well founded. This ab- 

 sorbing faculty is manifested also in the testacea which in- 

 habit the earth, and in those which sojourn in the waters. 

 I was able to estimate the quantities of oxygen absorbed by 

 the animals alone and by their shells; only I remarked, that 

 the absorption produced by the shells was slower than that 

 by the annuals. 



While engaged with these experiments, analogy suggested 

 •*io me the idea of a body which was indeed of a different 

 kind, but which seemed worthy of attention. The shells of 

 the testacea are formed by two substances, one ttrreo-calca- 

 reous, the other animal. The shells of the eggs of birds arc 

 formed of these two substances ; Is it not possible, or rather 

 jirobahle, thought I, that this absorbing principle may reside 

 only in these coverings r I actually found it in the shells of 

 all the eggs which I subjected to experiment; and as I have 

 a proof that a part of the oxygen absorbed by the shells.of 

 testacea passes into the animals which inhabit them, it is 

 probable that it concurs to the preservation of their life. I 

 think I have proofs of this sufficiently strong to show the 

 passage of the oxygen 2;as into the interior part of the egg 

 in order to vivify it, and to concur to the development of the 

 germ it contains. 



I cannot leave these considerations on the shells of testa- 

 cea and of eggs, without throwing some light on a point in- 

 s parable from tiitir nature. Thpir constitvicnt principles, as 



we 



