126 THE NORTHERN MICROSCOPIS'. 
The ‘Preliminary Report of the Havana Commission to the 
National Board of Health,” U.S., upon malarial or yellow-fever, 
contains the following :—“ If there is any organism in the blood of 
yellow fever patients, demonstrable by the highest powers of the 
microscope as at present perfected, the photo-micrographs taken 
in Havana should show it. Vo such organism ts shown in any 
preparation photographed immediately after collection. But in certain 
specimens kept in culture cells, spherical bacteria made their 
appearance after intervals varying from one to seven days.” 
Another source of difficulty consists in the imperfection of our 
optical apparatus. Cohn expresses an opinion in these words :— 
**So long as microscope makers do not place higher powers at our 
disposal, without immersion ; when in the domain of bacteria we 
shail still find ourselves in the situation of a traveller who wanders 
at twilight in an unknown country. The light of day no longer 
‘available to enable him to distinguish objects, he becomes 
conscious that notwithstanding all his precautions he is liable to 
lose his way.” 
The presence of organisms in the atmosphere seems first to have 
been mentioned by Ehrenberg in the year 1830; and, in 1847, he 
published his celebrated treatise upon the subject. The cholera 
epidemic in the year 1848 caused him to examine the dust 
deposited from the atmosphere, but as the higher powers of the 
microscope were not developed in his time, too much faith should 
not be placed in these and similar observations. 
In 1849, some peculiar cells, stated to be due to the cholera 
fungus, was noised abroad by Swayne and Brittan, which caused 
the Royal College of Surgeons to appoint a sub-committee to 
examine the question, and they arrived at the conclusion that 
bodies presenting the so-called characteristic forms of cholera 
fungi are not to be detected in the air of infected places. 
Dr. Dundas Thompson in the same year, with the co-opera- 
tion of Mr. Rainey, collected solid particles from the air by 
aspiration through distilled water; but we have already pointed out 
that this method may be a source of error. About the same time 
Lord G. S. Osborne examined air by exposing slips of glass 
moistened with glycerine, over cesspools, gully holes, and other 
places near houses in which cholera appeared. He caught spores 
of fungi and minute germs which he termed “ aérozoa.” 
The Rev. M. J. Berkeley, F.R.S., in his “Introduction to 
Cryptogamic Botany,” published in 1857, makes allusion to the 
fact of the spores of fungi being wafted immense distances out to 
sea, Gigot, in 1859, published his ‘Recherches sur la Nature des 
Emanations Maricageuses,” and Quatrefages, in the same year, 
tecognised the presence of spores in great numbers. Pouchet 
then appeared on the scenes, and the result of his numerous 
