114 
W. L. RHOADS. 
have selected a subject far beyond the limit of my brief experi¬ 
ence, and those practitioners who fail to keep abreast with the 
current of veterinary and medical literature are losing much 
valuable information on this topic of most vital importance. I 
feel no question in medicine of late years has occupied so much 
space and thought or caused so much scientific research and ex¬ 
periment as the origin, development and communication of 
disease. We to-day have a knowledge, though yet limited, of 
organisms infinitely small, the existence of which was not suspec¬ 
ted by the ordinary practitioner till within the last few years. 
When we consider that some of these germs when mature are 
but seven one-thousandths of an inch in length and their breadth 
scarcely one-fifth their length, our ignorance of them in the past 
is not surprising. We now feel that we understand fairly well 
the relation such organisms bear to our own as well as the 
organisms with which we have to deal in the lower animals in 
health and disease. 
It is true “ many of the lower organisms ” both animal and 
vegetable, have for years been recognized as the direct cause of 
local maladies, both external and internal, for many of these 
parasites were of sufficient size to be in the aggregate seen by the 
naked eye or a low power lens. When we realize that many of 
the most potent germs do not exceed T - 0 Vo' m - m * diameter, these 
bodies so light and small are easily influenced by movements of 
wind, rain or change of temperature, this coupled with the fact 
that no so-called case of spontaneous generation has withstood 
rigid investigation. We have a faint idea of the great good done 
by Bonnet, who between 1740 and 1793 advanced the theory of 
universal dissemination of seeds and spores known as the pre¬ 
existing germ theory (this is the oldest and probably the most 
widely accepted theory ever known in history of medical science). 
During this same period Needham came to the conclusion that 
infusion of organic matter placed in hermetically closed vessels, 
after boiling, brought forth minute organisms; this is known 
as the vegetative or producing force theory. The method of 
study introduced by Needham forms the basis of all subsequent 
