THE MICROBES OF HUMAN DISEASES. 189 
The same observer was able to point out the spores, 
which are only visible under a magnifying power 
of 1000 diameters, and which succeed to the spirilla 
during the remittent period. Moreover,a monkey was 
successfully inoculated with the disease at Bombay, 
and after the lapse of five days spirilla were found 
in the animal’s blood. 
Yellow fever has not yet been sufficiently studied 
in the countries in which it prevails, but there can 
be no doubt that it is likewise produced by a special 
schizophytum. Originating, as it appears, in North 
America, probably in the delta of the Mississippi, this 
disease has been spread by maritime commerce over 
the whole intertropical zone of the globe. The centres 
of infection are always on the sea-board, at the mouths 
of great rivers, from which we conclude that its special 
microbe is found in its free state in the brackish 
marshes formed at river-mouths. 
The medical men of Rio de Janeiro, and particu- 
larly Freire, have lately described and published illus- 
trations of microbes said to have been observed by 
them in the feces of patients attacked by yellow 
fever. But their drawings are for the most part 
fanciful, and betray great inexperience in the methods 
of research and in microscopic examinations; for 
instance, the air-bubbles, unskilfully interposed in 
the preparations which their author thought worthy 
of photographic reproduction, figure as microbes. 
Thanks to the accuracy of photography, which leaves 
