Robert Koch. XX1 
One cannot emphasise 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 eleven important human 
diseases—tubercle, cholera, typhoid, diphtheria, erysipelas, tetanus, glanders, 
pheumonia, epidemic meningitis, 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 infective agent in 
_ tuberculosis, whilst diphtheria and typhoid were being investigated by his 
assistants, Loeffler and Gaffky. The work of Klencke and Villemin and the 
further 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 body. Miliary tubercles were examined 
microscopically for some signs of a microbe, but for long without success. 
At last, by a modification in the method of staining, a fine bacillus was 
discovered, and its presence in the majority of preparations established. 
Efforts to grow the organism in pure culture at first failed, but subsequently, 
by infinite patience, he succeeded in growing it upon coagulated serum. 
Once isolated and grown upon a succession of media, the establishment, of 
the bacillus as the etiological factor presented no difficulty, and at the 
Physiological Society in Berlin on March 24, 1882, Koch presented the 
proof that he had discovered the cause of one of the most widespread 
and dreaded of human diseases. 
From the discovery of the cause of a disease, its prevention or cure does 
not necessarily follow, but in the campaign against an enemy it is of first 
importance to be acquainted with his nature and peculiarities. Koch 
interested himself, at once, in studying the life-history and methods of 
warfare of the tubercle bacillus. These studies were, however, interrupted. 
Cholera was in Egypt and threatened Europe, and the German Govern- 
ment organized a Commission, with Koch as leader, to proceed to Egypt 
to study the disease, and draw up recommendations for dealing with it, 
should it reach Germany. Shortly after reaching Egypt the outbreak there 
ceased. In the meantime, however, Koch had obtained important informa- 
tion leading him to suspect a particular comma-shaped bacillus as the 
specific cause of the disease. The material for the furtherance of his 
inquiry having failed in Egypt, Koch proceeded to India, where cholera is 
endemic, and completed his investigations. He satisfied himself that the 
comma bacillus was the constant companion of the cholera disease, that 
its abundance was commensurate with the severity of the attack, and that 
it penetrated beneath the epithelium in the affected part. He never _ 
succeeded in obtaining it from the healthy or diseased intestine, other than 
in the case of cholera. It was comparatively easy to obtain it in pure 
culture, and its characteristics were studied, but the completion of the 
evidence to convict this organism was lacking, as a true cholera process 
