ROBERT KOCH. 653 
Koch’s interest in traumatic infectious diseases seems to have been 
stimulated by the disasters due to these causes among the wounded 
im the Franco-Prussian War. The results of Lister’s antiseptic 
methods had demonstrated that means directed against the infec- 
tion of wounds with microbes obviated these diseases. Micrococci 
and bacteria had frequently been found in pus, diphtheritic ulcera- 
tion, in. the tissues at the edge of advancing erysipelas, and in pyemic 
deposits. Microorganisms had also been discovered in the blood of 
relapsing fever and puerperal fever. Further, Coze and Feltz and 
Davaine had inoculated rabbits with the blood of patients dead of 
puerperal fever, and had succeeded in carrying on the infection 
through successive generations of these animals. Nevertheless, the 
evidence that a particular organism was the cause of a particualr 
disease was far from conclusive. Many observers concluded that 
bacteria were universally present in the normal body. Others failed 
to find any organisms in obviously septic conditions. There was no 
practicable means of separating one coccus from another coccus, and 
bacteria of identical appearance were found to be associated with a 
variety of diseases. The parasitic nature of traumatic diseases was 
probable, but unproven. 
Koch began his work on traumatic infective diseases with the con- 
viction that the most fruitful line of investigation would be a com- 
parative one, namely, to induce septic infections in animals and see 
whether they would ‘‘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 organism. Moreover, if the same material con- 
taining 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 im one 
animal and not in a neighboring 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, 
