BACTERIA. 10s 
The blood of animals suffering from splenic fever is found to 
contain multitudes of Bacteria almost indistinguishable in ap- 
pearance from the still condition of the Bacillus of hay-infusion, 
but differing totally in properties. The Bacillus of hay-infusion 
if injected into the body of a healthy animal produces no morbid 
symptoms; the Bacillus of Distemper, on the other hand, infal- 
libly produces an attack of the disease. Again, the Bacillus of 
Distemper will not live in hay-infusion. The two are therefore 
considered to be distinct species; the hay-bacillus is called B. 
subtilis, the distemper-bacillus B. anthracis, “anthrax” being 
another name for the disease. 
The history of this distemper was worked out by a German 
physician named Koch. He found that all the time the disease 
was going on, the bacilli multiplied in the usual way, by division, 
in the blood and tissues; but that when the animal was dead, 
the process of spore-formation began. He also found that blood 
containing bacilli, without spores, retained its infective character 
for about five weeks; that is, that for five weeks after being 
taken from the body of an infected animal a drop of blood in- 
jected into a healthy one produced an attack of the disease, but 
that after that time it was harmless. On the other hand, it was 
found that blood containing spores retained its power of pro- 
ducing the disease for many years, 
You will see at once how this bears on the ordinary infectious 
diseases to which mankind are subject—on the fact, ¢. g., that 
scarlet-fever infection will hang about a house for many months 
if the most elaborate precautions are not taken for disinfection 
by stripping off old wall-papers, washing with carbolic acid, 
painting or whitewashing, etc. 
Positive proof that Bacillus anthracis was the cause of Dis- 
temper was afforded by cultivating the organism in various nu- 
trient liquids—apart from the animal body,—and finding that after 
living in this way for many generations, the injection of a drop of 
fluid containing it invariably produced the disease. It must be 
noticed that the effect of inoculation with disease-bacteria is quite 
different to that of an ordinary poison. In the latter the effect is 
proportiona] to the dose ; with the bacteria, on the other hand, 
an infinitesimal dose produces all the effects, since the organism 
immediately begins to multiply in the body of the subject. 
It is proverbially difficult to fight an unseen enemy, and it 
will be evident to you all that a very important step was taken 
when the full history of the contagion of splenic fever was thus 
made out. Further experiments were, however, attended with 
even more practical results. 
Splenic fever is fatal both to hoofed animals such as sheep, 
cattle, etc., and to rodents or gnawing animals, such as mice, 
rabbits, and guinea-pigs. Dr. Burdon-Sanderson found, some 
years ago, that a calf inoculated with the blood of a guinea-pig 
which had died of the fever, took the disease in a mild form, not 
fatally as it would have done if inoculated with the diseased 
blood of one of its own kind ; the difference was somewhat simi- 
