Iie 
On Pasteur’s Method of Inoculation and its 
Hypothetical Explanation. 
‘© TN Nature’s infinite book of Secrecy,” the bacillus and kindred orga- 
nisms form an interesting, and of latea much-read, page. Their 
very minuteness, and the difficulty of studying them, lends an 
additional fascination; and they rise into painful importance in the 
light of the modern view that they are the cause of disease. 
Since splenic fever was first attributed to the bacillus by the two 
French observers, MM. Davainne and Rayer, in 1861, one disease 
after another has followed, until finally the cause of influenza has. 
revealed itself under the microscope of the investigator. To give a 
list of diseases now attributed to it, would be to compile a page 
from a medical treatise. . 
All this renders the bacillus of paramount interest, yet a still 
greater interest attaches to the extraordinary pathways to health 
pointed out by the brilliant researches of Pasteur. I allude to his. 
well-known system of inoculation in order to confer immunity 
from disease. 
The foundation of Pasteur’s process is the cultivation of the 
microbe—bacillus, micrococcus or bacterium—outside the animal body 
in a suitable medium. Various substances—meat broth, sugar and 
peptone, Liebig’s extract, &c.—are used in which to grow the microbes. 
These liquids, or solids, must be sterilised—that is to say, heated 
until all germs which may have existed in them have been destroyed 
—and afterwards protected from atmospheric germs by plugs of 
cotton wool. With these precautions it is found possible to obtain 
pure cultivations of any microbe which may be sown in the medium. 
Into a tube or flask, then, containing this medium a drop of blood, 
or fragment of tissue, from a diseased animal is introduced. The 
microbe existing in it at once increases in numbers, and soon renders 
the medium turbid. A drop of this first cultivation introduced under 
the skin of a healthy animal reproduces the original disease with 
which it was associated. To obtain a second cultivation, a drop 
from the first is placed in another portion of the medium, where 
the microbe increases as it did in the first. Proceeding in this 
way, a succession of cultivations may be obtained. Now Pasteur 

