18 BACTERIOLOGY. 
serums are used successfully as preventives in many of 
the infectious diseases and as a cure in several, An 
acquaintance, therefore, with the main facts and results 
of bacteriology is as necessary to the education of the 
modern physician as a knowledge of anatomy, pathol- 
ogy, chemistry, or any of the allied sciences. 
But before entering into a detailed consideration of 
the subject, it may be interesting and instructive to 
review briefly the most important steps which led up 
to the development of the science, and upon which its 
foundation rests, in which we shall see that the vast 
results obtained by bacteriology were gained only 
through long and laborious research, and after many 
obstacles were met and overcome by indomitable per- 
severance and accurate observation and experiment. 
The first authentic observations of living microscopi- 
cal organisms of which there is any record are those of 
Athanasius Kircher, in 1671. This original investi- 
gator demonstrated the presence in putrid meat, milk, 
vinegar, cheese, etc., of ‘‘ minute living worms,” but 
did not describe their form or character. 
Not long after this, in 1675, Anthony von Leeuwen- 
hoek observed in rain-water putrid infusions, and in 
his own and other saliva and diarrheal evacuations 
living, motile ‘‘ animalcule ” of most minute dimen- 
sions, which he described and illustrated by drawings. 
Leeuwenhoek was a linen-draper by trade, living at 
the time of his discoveries in Amsterdam, but he prac- 
tised the art of lens-grinding, in which he eventually 
became so proficient that he perfected a lens superior 
to any magnifying glass obtainable at that day, and 
with which he was enabled to see objects very much 
smaller than had ever been seen before. ‘‘ With the 
