THE AIR ANr LIFE 543 



still ijeuetrate after the orb has left us. It may be said that many forms 

 of animal and vegetable life would disappear but for the vaporized 

 water in the air ; this will be enough to eonvey an idea of its importance. 

 The action of the numerous solid substances found in the atmos- 

 phere is as varied as their nature. Physically pure air is, in fact, a 

 myth, and can only be obtained in laboratories by using certain pre- 

 cautions. Even :it the highest altitudes in which the number of air- 

 microbes is small and where they are in most cases actually absent, as 

 are also vegetable or animal particles, there are always to be found 

 mineral dusts, very tinely pulverized, to be sure, some of which comes 

 from the ashes ejected by volcanoes or from the soil itself, and some 

 from the infinitesimal fragments of aerolites that have crossed our 

 atmosphere. We can easily iierceive these dusts with the naked eye 

 on looking at a ray of the sun when it strikes across a room. But if we 

 wish to thoroughly analyze them, we must resort to the microscope 

 and the aeroscope. We shall then find the most diverse elements; 

 desiccated animalcuhe, worms, rotifers, etc., vibriones, infusoria, frag- 

 ments of insects, of wool, scales from butterflies' wings, hairs, feathers, 

 vegetable fibers, mushroom spores, particles of pollen, of flour, of 

 dust from the soil, and finally microbes. But little interest attaches to 

 many of these fragments considered from the present standpoint, 

 although it is an interesting fact to know that pulverized matter of 

 volcanic origin, like that which was recently cast off by Krakatoa, can 

 remain for years floating in the air at very high altitudes and, by the 

 action of the winds, move around the earth and produce the luminous 

 pheiujmcna of so great interest that have been noticed by the physi- 

 cists of every country and that we all saw for ourselves a few years 

 ago. With regard to life, a matter of interest is the presence of grains 

 of pollen which being carried to great distances by the wind may event- 

 ually fecundate flowers of the same species ; the presence of the sj^ores 

 of cryptograms which promote the dispersion of that group; again, 

 the presence of numerous seeds so constructed as to be easily trans- 

 I)orted by air, thus promoting their dissemination. These seeds are 

 very light and provided with appendices that enable them to float in 

 air for along time and to travel over immense distances, and fljially to 

 be sown far away and thus expand ihe domain and habitat of the 

 species from which they sprang. Instances of this kind are plentiful 

 and it were idle to attempt a longer recital. Another matter of inter- 

 est is the presence of microbes. Many among them are innocuous, but 

 there are also some that are deadly. Cast off into the air by patients 

 affected by tuberculosis, smallpox, scarlet fever, measles, diphtheria, 

 or any microbian disease, taken from the ground on which contami- 

 nated matter has been thrown, these microbes are lifted and transported 

 by the air and scattered in every direction, near and far, in a trail of 

 death. They are particularly numerous in inhabited i)laces. At Mont- 

 souris, M. Miquel found from 30 to 770 per cubic meter, according to 

 .wind, season, etc., 5,500 in the Rue de Kivoli, from 40 to 80,000 in hos- 



