48 BULLETIN 106, U. S. DEPARTMENT OF AGRICULTURE. 
the infection must pass from the blood either through the placental 
filter or through the inter-cotyledonal uterine mucosa. 
To the hypothesis that the infection enters through the placental 
filter is opposed the size of the Bang organism, which is about that 
of the bacillus of tuberculosis, an organism which is not known to 
pass the placental filter. The failure of the Bacillus abortus to pass 
the placental filter is further evidenced by the investigations of 
McFadyean and Stockman, which show that the infection appears 
first in the utero-chorionic space, secondly in the the fetal fluids and 
the fetal alimentary canal, and lastly in the fetal blood, in reverse 
order to what we should expect under this hypothesis. 
If the infection be introduced into the blood to escape into the 
utero-chorionic space through the intercotyledonal mucosa, we 
would expect the invasion to occur indifferently at any, and perhaps 
multiple points. A study of the location of the recorded lesions on 
pages 44-47 denies this. 
Originally Bang held that the genital canal was the avenue of 
infection, in which case any phenomena resulting from the invasion 
should normally begin at the internal os and radiate therefrom 
forward. This is precisely what occurs with great uniformity. 
No recorded case presents evidence to the contrary. 
It has been noted on page 23 that the uterine cavity normally 
becomes hermetically sealed when the embryo is one-half inch in 
length. The state of the uterine seal was closely observed, especially 
for any indications of changes from bacterial invasion. At no time 
when the uterine cavity was healthy were we able to note any sign 
of injury, mechanical or bacterial, to its outer or vaginal end nor in 
its central portion, regardless of the presence of muco-pus in the 
vagina, or of well-marked chronic vaginitis or other lesions, but in 
those cases where the fetus had died prior to the slaughter of the 
mother the uterine seal showed more or less complete disintegration. 
When the abortion exudate was present, the uterine end of the seal 
was stained, softened, and undergoing solution. Ita ppears to us, 
therefore, that the infection of contagious abortion not only enters 
the uterine cavity through the cervical canal, but precedes the for- 
mation of the uterine seal. We believe that as a rule the infection 
is present in the genital tract in cows and in virgin heifers prior to 
breeding. 
Six 3-year-old heifers were subjected by us to an experiment. 
Three had calved once each; the other three were virgin heifers. 
For a few weeks prior to breeding, the genitalia of the six heifers 
and the bull were washed occasionally. After breeding, each received 
in the jugular vein vigorous cultures of the Bang abortion bacillus, 
with the following results : 
