104 JOURNAL OF SCIENCE. 
apparently so remote from all direct human interest—have 
begun what promises to be a complete revolution in the Science 
of Medicine. 
Most of the great applications of science begin in this way. 
A few enthusiasts work at some apparently insignificant subject 
from pure love of knowledge, often with the result of being looked 
upon by their contemporaries as a sort of harmless madmen. 
Indeed in times past such persons were generally considered 
more mad than harmless, and sometimes had to pay very dearly 
for their eccentricity. But it is usually found, sooner or later, 
that those who are supposed to have become mad with overmuch 
learning are the very men who finally succeed in turning the 
world upside down. 
In the present case the study of Bacteria has given birth to 
the Germ Theory of disease. 
It is a matter of common observation that certain diseases— 
scarlet fever, typhus, measles, diphtheria, small-pox, cholera, etc., 
are zzfecttous—that is, can be transmitted from person to person. 
Whenever an outbreak of one of these diseases is thoroughly 
investigated, it can always be traced to some definite cause, such 
as the arrival of an infected person in a previously healthy locality. 
In all diseases of this sort a regular series of stages is gone 
through: after the complaint has been “caught,” there is a fe- 
viod of incubation, during which no morbid symptoms are mani- 
fest ; then the characteristic symptoms of the particular disease 
appear, the patient sickens, and the symptoms develope until 
the paroxysm of the disease is reached. Then, unless death 
supervenes, there is a remission of the morbid symptoms, the 
patient becoming gradually convalescent. It is at this period, 
however, that the risk of infection is greatest. But the patient 
himself is usually safe for the future from this particular disease. 
There is a close analogy between the course of these diseases 
and the putrefactive changes in hay-infusion produced by Laczllus 
subtilis: the spores found in the hay remain latent for a time, 
z.¢. until they are thoroughly soaked with the fluid and rendered 
fit for germination ; then the bacilli gradually increase until 
putrefaction is at its height ; a scum forms in which they elon- 
gate into filaments and form spores, the active bacilli in the fluid 
gradually diminishing. Hereafter the fluid is no longer able to 
support the existence of B. sudtilis ; it may, however, support 
that of other putrefactive organisms, and it is itself virulently in- 
fective. 
Ofall diseases belonging to this class the one which has been 
most thoroughly worked out is Splenic fever, or Distemper as it 
is sometimes called. It chiefly attacks cattle, sheep, etc., but 
sometimes also man. Its fatal character is such that ina single 
district in Russia, in a period of three years, it caused the death 
of 56,000 horses, cows, and sheep, and of 528 human beings. It 
is so infectious that in any place where there has once been an 
epidemic the contagion seems to hang about for years, causing 
continual fresh outbreaks, | 
