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often find organisms A, B, and C in healthy animals, and therefore conclude they
are harmless. But we also invariably find organisms, undistinguishable in shape
from A, B, and C, present in the very first stage and throughout the course of diseases
1, 2, and 3. A always abundant in 1, never in 2 or 3 ; B always abundant in 2, never
in 1 or 3 ; and 0 always abundant in 3, but never in 1 or 2. The blood of 1, 2, and
3, containing the organisms A, B, and C, if put under the skin or into the stomach of
healthy animals, will invariably reproduce 1 + A, 2 + B, and 3 + C, but not other
associations. Again, if we destroy A, B, C, or remove them from the blood of 1, 2, 3,
by filtration, and then inoculate healthy animals with the blood so treated, we shall
either reproduce the disease in a very mild and modified form, or else not at all. A
pure chemical virus would be in a state of solution and would not be in the least
affected by the filter. From which results we conclude that the organisms A, B, and
C are the causes of the diseases 1, 2, and 3, though from other observations we find
that organisms, undistinguishable from A, B, and C in appearances, are harmless.*
25. Those who believe that these organisms cause the diseases with which they
are associated do not agree as to how the cause is effected. There are three theories
of explanation. 1st—That they block up the smallest capillary blood vessels and
so cause congestion and local inflammations, &c. 2nd—That they depuriate the blood
by absorbing the oxygen necessary for the performance of the vital functions of the
animal economy. 3rd—That they secrete from themselves something that is noxious
and which vitiates the blood, and while they are in the blood they reproduce this
faster than the excretive organs of the patient can get rid of it. The 1st and 2nd
theories are not applicable to the surra parasite, which most probably operates
according to the third theory.
26. B. Remote causes.—The proximate cause of surra disease being the character-
istic parasite in the blood, the remote causes are the conditions which bring the parasite
into the system of the animal. If the fly which I mentioned, or any other, propagates
the disease by inoculation, it is one of the remote causes. The parasite of surra is so
new to science, it has not yet been thoroughly studied, we know nothing of its natural
history excepting its appearance in the blood ; we know it must come from without,
but how or from whence, we know not. I approach this subject, therefore, with the
greatest caution and diffidence : my opinion is based upon a few facts, provisionally',
until more facts are obtained to confirm or to correct it.
27. All the lowest forms of organic life, whether of the animal or vegetable
kingdom, must have water more or less stagnant for their development: whether it is
a chemical or an organic solution they breed in, their growth is arrested as soon as the
water is evaporated. Water, more or less stagnant, and more or less impregnated
with a chemical or organic solution in a certain degree of temperature, is essential to
their origin and development. An organic fluid, such as blood or the infusion of hay
or grass, is more favorable than a chemical solution. Some of them have several
states of being ; when they are transferred from a dead solution into a vital fluid such
as the blood, they assume new forms; so that we must not always look without for
the forms we find within the animal economy. The parasite of disease may exist in
a pond or in moist ground in a very different form to what we find it in the blood.
Therefore from analogy I assume that the parasite of surra has its original normal
development in moist ground, stagnant ponds, or slow running streams, and I further
assume that it exists in such places in a different form to what it does in the blood ;
for, while I readily succeeded in propagating it by transference to living healthy blood,
I have in two experiments failed to develop it by transferring it with a little blood
into well water or into infusion of hay. The next fact is this—the spores and ova of
a great many of these low organisms survive for an indefinite period in the dry state,
in which state they may be conveyed by wind and other agents to distant places
where they will develop under favorable conditions of moisture and heat. In wet
seasons they remain localised to a greater extent than in dry hot seasons, for they
cannot be blown about; but those scattered in a dry year may remain in dry places
all over the country, until the rain of the following year comes to develop them ; and
then people often think the rain brought the pest, whereas the germs were brought
* The parasitic organisms A, B, and C may cause disease by secreting a chemical virus, or by causing some kind
of fermentation in the blood, &c.
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