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277 



small even in a volume of air equal to ten cubic centi- 

 metres — which^ in reference to such experiments^ must 



be 



considered something considerable. 



In such a 



eggs 



volume of air I have not yet met with anything which 

 could be supposed to be either starch-granules^ 

 of Infusoria^ or spores of Mucedine-as^.' 



It also occurred to M. Pouchet that the nature of the 

 solid materials floating in the air of different localities 

 might be tested by examining the respiratory passages of 

 different animals — and more especially those of birds, in 

 which intercommunicating air-sacs ramify extensively 

 throughout the osseous system. He examined, therefore, 

 with the greatest care those bones of birds which were 

 most pervious to air ^ since corpuscles or fragments of 

 any kind when once they had been introduced into such 

 cavities would be likely to lodge, on account of the 

 great irregularities of their surface 2. He says : — ^When 

 studied in this manner, the respiratory apparatus gives 

 us a faithful idea as to the life of these animals. It not 



^ 'Compt. Rend.' torn. li. p. 534. And yet, making use of a single 

 cubic decimetre of this very air taken either on the sea between Sar- 

 dinia and Sicily, or from the top of Mount Etna, M. Pouchet always 



obtained immense legions of Infusoria in his solutions after a very short 

 time. 



^ M. Pouchet says (*NouveIles Experiences,' p. 79) :— 'Pour recueillir 

 les corpuscles aeriens des os pneumatiques des oiseaux, j'enfonce le tube 

 d une seringue dans Touverture par laquelle Tair penetre dans leur cavite, 

 et je coupe Tos vers I'extremite opposee. L'eau injectee d abord douce- 

 ment puis ensuite tr^s-violemment pour entrainer jusqu'aux moindres 

 debris atmospherique est refue dans des verres et examinee/ Every 

 precaution was also taken to avoid admixture of particles from the atmo- 

 sphere at the time of examination. 



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