Pathology. Bacteriology. Franck attributed the disease to leptothrix vaginalis, but subsequent observers failed to substantiate this.
The Scottish Abortion Commission isolated five different bacteria from the abortion membranes and vaginal mucus, but failed to identify any one of these as, by itself, capable of causing the disease.
Nocard found in the fibrino-purulent matter between the chorion and womb in aborting animals a micrococcus occurring singly or in chains, and a short, delicate bacillus isolated or in pairs. From the absence of evil effects between pregnancies he opines that the germs grow in the membranes only, and do not affect the womb nor the general system. He recognizes, however, that they survive in the womb from one pregnancy to another in the complete absence of these membranes.
Galtier, on the contrary, conveyed the disease variously by the inoculation or feeding of the milk or abortion membranes to sheep, goat, pig, rabbit and Guinea pig, and accordingly claims that the general system of the pregnant animal is infected, and that the germs can be conveyed through the blood to the womb. In deducing this from feeding experiments he appears to make too little account of the ready infection through proximity of the anus and vulva.
Chester, of Delaware Agri. Experiment Station, found in the fœtal membranes of aborting cows a bacillus, which in form and habits of growth closely resembled the bacillus coli commune. In the fermentation test, however, it showed a marked difference.
Inoculated on rabbits it did not prove fatal. Injected into the vagina of a healthy pregnant cow it caused slight catarrhal discharge for four or five days, but the calf was carried to full time six and a half months later.
Bang found in aborting cows, between the womb and fœtal membranes, a considerable odorless, gelatinoid, liquid exudate, and some pus cells. There was active catarrh of the uterine mucosa which often carried the disease over into the next pregnancy. In the exudate he found a number of very minute nonmotile bacilli (1 to 3μ), which stained readily with aniline colors, excepting in a vacuole or nucleus which was less deeply pigmented. This bacillus grew well in serum glycerine bouillon, and more sparingly in serum-gelatine agar. In the latter it showed a remarkable peculiarity which serves to identify it readily from other microbes, in two successive zones of luxuriant growth at two different depths, with an intermediate clear zone, in which little or no growth took place. It seems to prefer a greater or lesser supply of oxygen (21 or 90:100) without being able to adapt itself to the intermediate condition. As already stated it produced abortion in the cow in 21 days after injection into the vagina. It also induced uterine catarrh and abortion in ewes, goats, rabbits, Guinea pigs and mares when injected into the vagina. From the vagina it usually reaches the womb, but not always. In several cases in which it was injected subcutem or intravenously it caused hyperthermia, and was later found in abundance in the interior of the womb and fœtal membranes, and in the bowels of the fœtus. The microbe is, therefore, capable of living in the blood and affecting the womb by whatever channel it may enter the system.
V. A. Moore and the present writer made a series of experiments at the New York State Veterinary College. In the fœtal membranes and uterine mucus of a number of cows, aborting in different parts of the State and therefore long distances apart, we found a bacillus that in form and culture-experiments closely resembles bacillus coli commune. This was nearly always in pure cultures, and in the few cases showing other microbes, these were only such as inhabit the healthy vagina. Our bacillus was never found in the womb nor fœtal membranes of cows that had calved at the full period in healthy herds. It agreed in most respects with the bacillus found by Chester, but differed somewhat in fermentation tests. It differed also in proving fatal to rabbits when inoculated on these animals. Injected in the form of cultures into the vagina in three old pregnant cows it continued to live on the mucosa, producing more or less catarrh and muco-purulent discharge in the different cases, yet all three carried the calf to full time, one having calved on the 123d day after injection, the second on the 167th, and the third on the 190th.
The results obtained at the Delaware College Experiment Station and the New York State Veterinary College, do not differ so seriously, as either one does from those obtained in Europe, by Nocard, Bang, and the Scottish Abortion Committee. The facts that the same germs were found, either in pure cultures, or exceptionally, along with the normal microbes of the healthy vagina, in the womb, and fœtal membranes of every aborting cow, that they were never found in the healthy cow which had calved at full time, and that the generative passages were the seat of a catarrh, alike in the cows that aborted and in those that were inoculated with the abortion discharges, but did not themselves abort, are all but conclusive that this microbe is the essential cause of the abortion.
The single objection to this view, namely that the inoculated cows did not abort is explained by the fact that in the New York abortions it is the rule that the calf is carried six or seven months from the date of impregnation (the date of the presumptive infection) to that of abortion. It is to be further borne in mind that our experimental cows were old, and may have passed through the disease before and become in some measure immune, that they were dry during the experiment, and were subjected to no extraneous excitement that would predispose them to abort. The presumption is that had the experiments been started earlier in the gestation, the abortion would have come in due time. The microbe maintained its hold on the mucosa and continued to advance up to and beyond parturition.