134 rOUCHET, ON ATMOSPHERIC MICROGRAPHY. 



with a sharp instrument either in the dead body or of a 

 living person. 



All these observations, if it were needed, might be sup- 

 ported by biological proofs. Until the contrary can be 

 shown experimentally, it may be said that the air is so 

 rarely the vehicle of ova, and the dust so rarely their recep- 

 tacle, that when the latter is subjected to an elevated tem- 

 perature, it is no less fecund in animalcules than that which 

 has not been heated ; which would not be the case, were the 

 hypothesis of aerian dissemination of ova founded in truth. 



I have often repeated the following experiment. I have 

 taken 3 grammes of an ancient dust, and placed it in a 

 thin tube, heated to 215° C, in an oil-bath, for an hour and 

 a quarter. The dust has afterwards been put into 30 

 grammes of artificial water, and the whole covered with a 

 bell-glass. At the end of five days, and at a mean tem- 

 perature of 20° C, the water was crowded with animalcules of 

 large size — CoJpoda and Paramoecium. The same result takes 

 place with dust which has not been heated. What has been 

 taken, therefore, for ova deposited from the atmosphere, was 

 not really such ; for, in that case, the dust which had been 

 heated would have been infertile, the germs contained in it 

 having been killed by a temperature of 215° C. 



Another very simple experiment also proves that it is 

 impossible to discover any living germ in the atmosphere. 

 By means of an inhaling flask I caused 100 litres of air to 

 pass through a safety tube whose bulb contained two cubic 

 centimetres of distilled water. At the end of eight days I 

 was unable to discover a single animalcule or ovum in this 

 small quantity of water, in which the latter, themselves, could 

 not escape observation, now that they have been completely 

 described and measured, and are well known in several species. 

 On the contrary, if I place in a cubic decimetre of distilled 

 water 5 grammes of a fermentable substance, sheltered 

 by a bell-glass having a capacity of one litre, at the end of 

 eight days, and at a temperature of 18" C, the whole surface 

 of the water is occupied by incalculable myriads of ani- 

 malcules. 



The memoir concludes with the detail of particular observa- 

 tions on dust collected in the following localities : 



Tower of Georges d'Amboise, at Rouen. Interior of the 

 Abbey at Fecamp. Ruins of Thebes. Tomb of Ramses 1 1. 

 Sepulchral chamber of the Great Pyramid. Temple of ^ enua 

 Athor, at Philoe. Temple of Scrapis, atPuzzuoli. Skull of 

 a mummified dog, from the subterranean vaults of Beni- 

 Hassan. The cabinet of a Jewish antiquarian at Cairo. 



