A few drops injected into the peritoneum of a Guinea pig, or veins of a rabbit, killed in six to eighteen hours with the lesions of hæmorrhagic septicæmia which characterize the most acute cases of white scour. The blood and viscera swarmed with the microbe.
A calf one day old had 3cc. of the culture injected into the jugular, the temperature rose in six hours, and in twenty hours the subject lay with sunken eye, retracted abdomen, a temperature of 95° F., and having the bed saturated with a yellowish, fœtid, fæcal liquid. Death took place 30.5 hours after the injection and all the lesions of acute white scour were met with.
A second calf four weeks old, which had already suffered from white scour and recovered, had an injection into the jugular of 10cc. of the same culture. In six hours he suffered a slight rise of temperature, was dull and breathed short, but in twenty hours he was completely recovered, full of life and appetite.
In other casual and experimental cases, Nocard found that when death occurred within one or two days the symptoms and lesions were mainly those of hæmorrhagic septicæmia and white scour, whereas if the calf survived several days, the impaired resistance of the tissues invited the invasion of a variety of other germs from the intestines, and infective inflammation of the lungs, joints and other organs were brought about by such secondary invasions.
An important question is as to the direct source of the primary (Pasteurella) infection. The concentration of the acute cases on the alimentary canal would strongly suggest infection through the food which in this case means the milk. But careful bacteriological examination of the milk of the dam of a calf that had just died of white scour, and of other milk secured with careful precautions from cows in an infected stable, showed that both were clear of the germ. Inoculations and culture experiments were equally fruitless.
This does not exclude the probability of the contamination of the milk, obtained under ordinary conditions, with the germ contained in the floating barn dust, or that which was adherent to the teat and udder.
Another suggestion is that the infection is derived from the infected womb prior to birth, but as Nocard justly says, if this were so, abortions would be much more prevalent, as the rapidly fatal issue of the disease would determine the prompt death of the fœtus and its expulsion. The coincidence of abortion and white scour in a herd is not uncommon, and in such cases intrauterine infection of the fœtus is not improbable, but in the great majority of cases no such coincidence exists.
We are thus thrown back on infection through the raw surface of the ruptured umbilical cord, as the rule in such cases. It may be that this has come from the vagina or vulva, but in the great majority of cases it is manifestly derived from the infecting bowel dejections and the dust caused by their desiccation. The extraordinarily rapid progress and fatal result of the acute disease, and the early abundance of the germ in the blood and liver, suggest that the microbe traverses the umbilical vein to the liver, and finding a congenial home in the blood is quickly distributed through the entire body.
Prevention must be based on the destruction and exclusion of the microbe.
A thorough disinfection of the stable with mercuric chloride has not given us uniformly satisfactory results, even when the building has been kept apparently almost immaculately clean. This argues a renewed infection through the fæces of the cows, yet it is the rule that the removal of the cow to a new or unused stable a few days before calving will usually secure the immunity of the calf. This method is however open to the objection that the removal to such calving stable of a succession of cows coming from infected premises soon introduces the infection and renders it as dangerous as the place they have left. To carry out such a plan therefore a number of new stables or sheds must be provided to be used in succession, as they become one by one contaminated.