654 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
The publication of these three papers raised the hitherto obscure 
physician of Wollstein to the first rank of scientific investigators, but 
they were merely the beginning of his scientific career. Their 
importance and the genius of their author was recognized by Struck, 
the enlightened director of the German health office, who invited 
Koch to accept a position in that department. The chemical and 
hygiene laboratories attached to the department had been exten- 
sively equipped, but bacteriology was naturally unprovided for. A 
room was, however, found for him, and in these humble surroundings 
he settled down to pursue his inquiries. He was soon joined by 
Loeffler and Gaffky, who became his first assistants. The three 
worked together enthusiastically in the one room, fitting up the 
laboratory, inventing apparatus, and improving methods. The 
great problem confronting them was to find a practicable means of 
obtaining a pure culture outside the body. Koch accomplished this 
by the simple expedient of adding gelatin to the nutrient medium. 
The gelatin-containing medium was inoculated whilst warm with a 
minute amount of the material, poured in a thin layer upon a plate 
and allowed to set. In this way bacterial colonies originating from 
individual microbes were obtained. Portions from the colonies were 
subsequently sown into separate tubes of broth or other fluid suitable 
for their growth. The discovery of this technique made advance 
possible. 
Another line of investigation undertaken at this time, on account 
of its importance in the technique of bacteriology, was concerned with 
disinfection and _ sterilization. The experiments of Koch and his 
pupils, made upon pure cultures of pathogenic bacteria, is the foun- 
dation upon which all later work on this subject has been built. It 
also led to the substitution of the more convenient steam steriliza- 
tion for dry heat. 
One can not emphasize too strongly to what a large extent Koch 
provided the tools of inquiry at each stage in the development of 
bacteriology, but he did not rest there. From 1880 onward followed 
a period of extraordinary activity. In a dozen years the etiological 
factor of 11 important human diseases—tubercle, cholera, typhoid, 
diphtheria, erysipelas, tetanus, glanders, pneumonia, epidemic menin- 
gitis, influenza, and plague, as well as numerous animal diseases— 
was discovered by Koch and his pupils. 
After the completion of his work on anthrax Koch’s individual 
efforts were directed more particularly to the discovery of the infec- 
tive agent in tuberculosis, whilst diphtheria and typhoid were being 
fered by his assistants, Loeffler and Gaffky. The work of 
Klencke and Villemin and the ieee experiments of Cohnheim and 
Salomonsen, had established that the disease tuberculosis was due to 
an infective agent which was capable of propagating itself in the animal 
