Later many vague speculations, based more upon
imagination than upon facts, prevailed, until Pas-
teur's investigations into bacteria as a cause for fer-
mentations led to his discoveries and proofs that the
infectious diseases owed their origin to bacteria.
46



n

I



THE RELATIONS OF BACTERIA TO DISEASE 47

At the present time the principal diseases known
to be due to specific microorganisms are : —

Class I. Septicaemia, gonorrhoea, Asiatic cholera,
leprosy, pyEemia, syphilis, influenza, bubonic plague,
pneumonia, diphtheria, tetanus, relapsing fever,
meningitis, typhoid fever, tuberculosis, glanders,
anthrax, malaria, sleeping-sickness.
Class II. To this class belong those diseases
caused by organisms which are yet unknown : small-
pox, foot-and-mouth disease, yellow fever, chicken
pox, hydrophobia (rabies), measles, mumps, scarlet
fever. Rocky Mountain spotted fever, typhus fever,
epidemic infantile paralysis.
The sources of the communicable diseases in
man are man himself and the lower animals ; the
majority are peculiar to human beinga, although
we contract anthrax from cattle, plague from rats,
tuberculosis in part from cattle, etc. Formerly it
was thought that the main sources of infection in
man were in water, air, soil, and food; and while
these may serve as vehicles for conveying infectious
materials, the source is usually in man himself.
No single species of pathogenic bacteria can pro-
duce disease in all animals, nor are the disease-
producing bacteria for animals the cause of disease
in plants. A bacterium may produce disease in



48 BACTERIOLOGV FOR NURSES

man and be harmless for cattle, and on the con-
trary, man is not susceptible to all the diseases of
cattle.
