Ka Obituary Notices of Fellows deceased. 
“breed true” upon successive reinoculations, controlling the experimental 
observations by careful microscopic examination throughout. He used for 
the purpose of infecting his animals putrid serum or bouillon. This, he 
found, contained a large variety of organisms of different sizes and shapes, 
which he was unable to separate from one another. He hoped that, 
implanted into the body of an animal, a selection might occur, and only 
those pathogenic for the particular species survive. His anticipations were 
justified, and the injection of small quantities of such materials was followed, 
in a number of instances, by the development of a fatal illness with the 
presence in the blood of one only of the many forms present in the original 
material. He was able to carry on the disease from one animal to another, 
always with the same symptoms and the presence of the same organisin. 
Moreover, if the same material containing a variety of organisms were 
injected into animals of different species, one microbe flourished in the one 
species and another in the second, showing that a particular microbe could 
establish itself in one animal and not in a neighbouring species. 
The animal body is, as Koch said, an excellent apparatus for pure 
cultivation, and he succeeded to some extent in doing what had been the 
stumbling block to all progress, namely, to isolate one organism from another. 
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 were recognised by Struck, the enlightened Director of the 
German Health Office, who invited Koch to accept a position in that depart- 
ment. The chemical and hygiene laboratories attached to the department 
had been extensively 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 gelatine to the 
nutrient medium. The gelatine-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 sterilisation. The experiments of Koch and his pupils, made upon pure 
cultures of pathogenic bacteria, is the foundation upon which all later work 
on this subject has been built. It also led to the substitution of the more 
convenient steam sterilisation for dry heat. 
