6
less extent to sheep, goats and many small animals. Country-bred horses are
immune but donkeys succumbed to inoculations of virulent blood. In some
districts in this country, the disease is said to appear sporadically during the
whole year, especially those localities which are marshy or intersected by
rivers. The disease, however, becomes epizootic, as a rule, during the monsoon
and during or after the Christmas rains. Several types of this disease may be
encountered in the field, viz., (i) Superficial or Cutaneous ; (ii) Thoracic;
(iii) Intestinal; and these in acute or chronic form. During the course of
these researches, it has been found that hill animals are the most susceptible to
Hæmorrhagic Septicæmia. Buffaloes and plains bovines coming next, in the
order mentioned. It must, however, be distinctly recognized that the
" materies morbi " differs in virulence considerably in different outbreaks, and
further the susceptibility of the animals of various breeds exposed to the
" contagium" likewise varies. Consequently, the periods which intervene,
viz., the incubation period of the malady and that between the exhibition
of the first symptom recognisable and death, may also be found to vary
considerably.
Experimentally it has been demonstrated that one large drop of a virulent
broth culture of the organism of Hæmorrhagic Septicæmia inoculated
subcutaneously, was sufficient to bring about death respectively in buffaloes,
hill and plains bovines, in the following periods :—
(1) hill bovines in 23½ hours,
(2) buffaloes in 28 hours, and
(3) plains bovines in 28 to 42½ hours.
It will, therefore, be observed that there may be no time to treat acute
cases, which frequently exhibit no symptoms of the disease, or only for a short
period, i.e., several hours before death.
It is laid down that one attack of this disease gives protection against a
second one during the lifetime of the animal. We have found that animals
which have passed through one attack of the disease and recovered possess an
active immunity after an interval of two years, and this protection may be
found in future experiments to extend for a much longer period.
27. Preparation of Hæmorrhagic Septicæmia serum.—The organism of
this disease, as obtained in cultures from the blood of animals which succumbed
in the field, has been found to vary in virulence to an enormous extent.
Consequently, instead of utilizing several strains of the " causal agent " for
the purpose of immunizing the necessary animals for the preparation of a
polyvalent anti-bacterial serum, the same has been prepared at this Laboratory
from cultures of the organisms after passing them through a series of highly
susceptible animals until a minimal lethal dose had been arrived at. This
procedure was adopted with a view to insure the serum being possessed of
qualities capable, if possible, of granting in small doses a passive immunity
against the most virulent strain to be encountered in the field.
28. Summary of some results obtained with serum of bovines hyper-
immunized with the Causal Agent of Hæmorrhagic Septicæmia.—(i) The
disease does not appear to infect by the gastro-intestinal tract unless there is
an abrasion, for, animals drenched with large doses of virulent culture showed
no symptoms during a further period of two weeks. The majority of such
animals when tested with virulent culture at a later date succumbed.
(ii) Hill, in contra-distinction to plains, bovines require a larger dose of
the anti-bacterial serum to produce protection.
(iii) Plains animals respectively injected subcutaneously with a standard
dose of serum still possessed a full passive protection against the inoculated
disease after a period of four weeks, but those tested after seven weeks
succumbed.
(iv) The same standard dose, viz., 5 c. c. of serum failed to protect hill
cattle even for eight days. Such breed of cattle require a double dose (10 c. c.).
(v) Hill animals subcutaneously inoculated, by the simultaneous method
(with 5 c. c. serum + 0.1 c. c. virulent culture) succumbed to the disease like
ordinary unprotected animals.
(vi) Hill animals submitted to the simultaneous method (5 c. c. serum
injected intravenously, and virulent culture 35 minutes later subcutaneously)
were found to be protected.