MICRO-ORGANISMS IN RELATION TO MAN. 95 
longer time than will the ordinary vegetative cells from which 
they arise. 
It is now generally admitted that all infectious and con- 
tagious diseases, and probably many others, are due to the 
activity of micro-organisms, although it is only in a compar- 
atively few instances that any particular micro-organism 
has been conclusively proved to be the causal agent of a 
particular disease. 
As long ago as 1671, Lange expressed the opinion that 
measles and other fevers were the result of putrefaction 
caused by worms or animalcule growing in the body, and 
in 1683, Leuwenhoek, a native of Holland, described and 
figured, in material taken from the teeth and in various in- 
fusions, minute organisms which can now be recognised as 
bacteria. A little later, another physician, named Audry, 
replaced the worms mentioned by Lange, but really discovered 
by Kircher, by the newly described germs of Leuwenhoek, 
and, pushing the theory to its legitimate and logical conclu. 
sion, evolved a germ theory of putrefaction and fermentation. 
He maintained that air, water, vinegar, fermenting wine, old 
beer and sour milk were all full of germs; and that small-pox 
and other diseases, very rife about this period, were the result 
of the activity of these organisms. And, it is said, so much 
headway did he make that the mercurial treatment much 
in vogue at this time was actually based upon the supposition 
that these organisms were killed by the action of mercury 
and mercurial salts. About this time, too, it was first sug- 
gested that the dangerous character of marsh or swamp air 
was due to the action of invisible animalcule. In the early 
part of the eighteenth century, however, great ridicule was 
thrown upon this theory and it became discredited. It is 
however, noteworthy that Linneus firmly believed in this 
germ theory of disease. 
Much continued to be written during the next hundred 
years, a large mass of facts were accumulated, and the 
