100 MICRO-ORGANISMS IN RELATION TO MAN, 
and observation of the results, any unknown species can 
readily be identified. 
We are indebted to Dr. Koch, the eminent German physi- 
cian, for the introduction of this method of plate-culture, and 
he was able by its means to show the connection between a 
micro-organism and splenic fever or anthrax. This organism, 
Bacillus anthracis, in its relation to the cause of a specific in- 
fective disease in the higher animals and man, has been more 
thoroughly studied than perhaps any other bacterium. Its 
power of adaptability to various conditions, and its character- 
istic appearance, have favoured a careful and systematic study 
of its properties. In 1850, Davaine and Rayer observed 
microscopic rods in the blood of animals which had died of 
anthrax, but they did not appreciate the full significance of 
their discovery. Some thirteen years later, the former worker, 
stirred by the researches of Pasteur, came to the conclusion 
that the organisms were the cause of the fever. This met 
with much opposition, which was not set at rest until Koch 
applied the method of plate-culture to the disease, It was to 
the experiments of Koch on the great difference in sensitive- 
ness between the ordinary vegetative forms of the bacillus 
and its spores, and the rapid conversion of the latter into the 
former, that the method of intermittent sterilization, introduced 
by Tyndall, was due. 
Pasteur also examined the cause of anthrax or splenic fever, 
and he employed the method he had used with great success 
in his previous experiments. He isolated the organism from 
infected blood, cultivated it in a state of purity in artificial 
liquids, and then examined the action of these cultures on 
animals. When thus purified, it was found that a small 
quantity of the culture, injected under the skin of a rabbit or 
a sheep, proved fatal in two or three days, the animal dying 
with all the symptons of splenic fever. 
Both Pasteur and Koch experienced no difficulty in 
producing the disease in animals subject to it, by means of 
