132 POUCHET, ON ATMOSPHERIC MICROGRAPHY. 



Quatrefagcs lias taken for the ova of raicrozoa. It is the 

 most minute grains of this substance to which he refers when 

 he states, that he " could easily recognise in the dust" several 

 of those minute corpuscles of a spherical or ovoid form, well 

 known to all micrographers, and which involuntarily suggest 

 the idea of an extremely minute ovum.* This image is 

 correct, but the illusion is at once dissipated by the slightest 

 chemical test, which proves that the granules in question 

 can be nothing else than either extremely fine amylaceous 

 grains or siliceous particles, which I have frequently ob- 

 served, and which are of such extreme tenuity, as under the 

 microscope to present the appearance of transparent spherical 

 granules. 



Astonished at the comparative abundance of the amyla- 

 ceous particles which I found among the atmospheric cor- 

 puscles, and in order to obtain a rigorous demonstration of 

 the fact, I determined to examine dust of all ages and from 

 all localities. I have investigated the monuments of our 

 great cities, others on the sea-shore and in the desert ; and, 

 in the midst of the immense variety of corpuscles universally 

 noating in the air, have almost everywhere met with starch 

 in greater or less abundance. Gifted with an extraordinary 

 self-conservative power, time seems scarcely to affect it. 



However remote may be the antiquity of the atmospheric 

 corpuscles, starch still recognisable is found among them. I 

 have discovered its presence in the most inaccessible recesses 

 of our old Gothic churches mixed with the dust, blackened 

 by an existence of from six to eight centuries. I have even 

 found it in the palaces and subterranean chambers of the 

 Thebaid, where it would date probably from the epoch of the 

 Pharaohs. 



It may be affirmed, as a general proposition, that in all 

 countries where wheat constitutes the basis of food, its 

 starchy element penetrates everywhere with the dust, and is 

 found mixed with it in more or less considerable quantity. 

 It is more abundant in situations near the centre of towns 

 and at a low level, whilst, in proportion as we go to greater 

 distances from the great centres of population, and explore 

 the more isolated monuments, does the starch become leas 

 and less abundant, and its grains more and more minute. 

 I have been unable to detect any cither in the Temple of 

 Jupiter Scrapis, situated on the shores of the Gulf of Baise, 

 or in that of Venus Athor, placed on the confines of Nubia. 

 Nevertheless, I have collected some in subterranean temples 

 of Upper Egypt. 



* 'CompteB rend.,' Paris, L859, t. xlviii, p. 31. 



