Summary of conclusions:(1) The injection of spleen or gland pulp (of coarse or fine grain) into the jugular vein can be carried out with but little risk provided microscopical examination proves that such material is not contaminated with bacteria or micrococci
(2) The presence of an Endocarditis verrucosa, due to the injection of such material, was only noted in one instance, and that was a case of a double injection into the jugular vein of 20 c.c. spleen pulp.
(3) The highest percentage of artificial infection, calculated on both deaths and immunity due to such injections, was obtained by the intrajugular method (vide Table A).
(4) Of the intrajugular injections, the most certain method of transmission was noticed after the injection of coarse-grained spleen pulp, and coarse-grained spleen and gland pulp (mixed) (vide Table B).
(5) The percentage of survivals amongst the animals treated by intrajugular injections, arranged according to the amount of material used, was as follows :-
In the dose of:
40 c.c. Nil survived out of 1 treated 0 %
25 c.c 2 survived Out of 7 treated 28 %
20 c.c 13 survived Out of 41 treated 32 %
15 c.c. 3 survived Out of 9 treated 33 %
10 c.c. 16 survived Out of 31 treated 51 %
30 c.c 9 survived Out of 13 treated 70 %
5 c.c. 24 survived Out of 34 treated 71 %
(6) The results of the intrajugular injections in the different experiments, arranged according to the immunity conferred, vary from nil to 100 per cent. (vide Table C).
(7) The highest percentage of transmission was obtained by the addition of peptone to the material injected (compare Table D).
(8) The material which transmitted the disease in the majority of cases was taken from cattle suffering from East Coast fever, which had been killed from the 25th day onwards after the infestation of ticks, or fourteen days onwards after the first rise of temperature (vide Table E).
(9) The inoculation was either succeeded by (a) a typical East Coast fever reaction, ending in death, and accompanied with the presence of plasma bodies; or (b) by typical East Coast fever reactions, accompanied with parasites, and ending in recovery; or (c) by mild or irregular reactions, accompanied with the presence of parasites, and ending in recovery; or (d) by reactions indicative of East Coast fever, but without plasma bodies; or (e) by irregular reactions; or (f) by no reactions (vide Summary of Experiment and Tables).
(10) Of animals inoculated in various ways, and exposed to tick infestation or natural infection, the least mortality occurred amongst those which had shown plasma bodies in the lymphatic glands as a result of the injection (vide Table G).
(11) An observation of fundamental importance is the fact that an animal which contracted the disease from ticks (viz., in the natural way) contracted it a second time and died when exposed to natural infection on the veld. In other words, animals which have recovered from a natural attack, due to tick infestation, may contract the disease again, although this seems to be a rare exception.
(12) A further fact of importance is the observation that five animals which contracted the disease from the injection, accompanied with the presence of plasma bodies in the lymphatic glands, and recovered, again contracted East Coast fever when exposed to natural infection, of which three died and two recovered.
(13) In the foregoing experiments, 224 animals were used in all, of which 180 were injected either once only, or twice within sixteen days, and forty-four were injected repeatedly.
(a) Of the 180 animals, nineteen died, chiefly from accidents resulting from inoculation, the cause of death being septic pneumonia, due to embolism with contaminated material. Thirty-nine contracted the disease from the inoculation and died. Forty-seven contracted the disease from injection and recovered. Of these forty-seven, three died before they could be tested, three died of relapses, that is to say, again contracted the disease in the field (breakdowns in immunity), two showed relapses and recovered, and six died of other causes after the critical period of the test had elapsed. Twelve did not react typically to the injection, and died of other causes before they could be tested, or before the critical period of the test had elapsed. Sixty-three animals which did not react typically to the inoculation were tested by the infestation of ticks and exposure to natural infection; twenty-eight contracted the disease and died, three contracted the disease and recovered, and thirty-two proved to be immune. Of the thirty-five, eight died later of other causes.
(b) Of the forty-four animals which were injected repeatedly, fourteen died, chiefly from accidents resulting from inoculation, the cause of death being septic pneumonia, due to embolism with contaminated material. Seven did not react typically to the injection, and died of other causes before they could be tested, or before the critical period of the test had elapsed. Twenty-three did not react typically to the injection, and were tested by the infestation of ticks or by exposure to natural infection, of which fifteen contracted East Coast fever and died, and eight proved to be immune; of these eight, two died later of other causes.
(14) The final result amongst the inoculated animals that were exposed to tick infestation and natural infection is :-
One hundred and thirty exposed, of which forty-six died of East Coast fever from tests, and eighty-five survived the critical period of the test, the net result of animals which survived injection and tests being eighty-four out of one hundred and seventy, or 50 per cent.
(15) For the present, a practical method of inoculation, which can be reasonably expected to confer immunity to the extent of 60 to 70 per cent., would consist in the injection of a quantity of not less than 5 c.c. of spleen or of a mixture of spleen and gland pulp (coarse grain) taken from an animal in the last stage of the disease, mixed with peptone and injected intrajugularly. This method can be applied in all cases of emergency as a last resource, that is to say, in cases where there are no opportunities for dipping, or moving the cattle, the artificial immunization can be adopted in order to save the greatest possible number of animals.