4 
BACTERIOLOGY. 
the instruments and methods for studying germs at 
that time were inadequate. 
In the next thirty to forty years many new 
methods were introduced which marked a rapid prog¬ 
ress in the study of germs; for example, the use of 
aniline dyes for coloring germs so that they could be 
seen better under the microscope, and solid and fluid 
culture media on which germs could be cultivated and 
different kinds separated and studied. The develop- 
Fig. 1.—Anthrax bacilli. Spore formation and spore germi¬ 
nation. A, from the spleen of a mouse after twenty-four hours’ 
cultivation in aqueous humor. Spores arranged in rods like a 
string of pearls. X650. B, germination of spores. X650. C, 
the same, greatly magnified. X1650. ( Koch .) 
ment of these new methods was due chiefly to the 
genius of Koch, who also laid down certain laws or 
conditions which had to be fulfilled before any germ 
could be said to be the cause of any specific disease. 
The laws or postulates of Koch were: 
i. The same organism should be constantly pres¬ 
ent in that particular pathological condition. 
