286 BACTERIOLOGY. 
indeed, that it required the inoculation of the entire 
contents of the body to cause tuberculosis in guinea- 
pigs; moreover, only one or two of a litter were affected 
at one time. According to these experiments one would 
expect to find in man feetal or placental tubercular in- 
fection more common than it is, whereas it is extremely 
rare, even if the few cases reported be accepted as proven. 
Possibly the few bacilli which may be transmitted to 
the foetus do not find conditions favorable for their 
development, and, being so few in number, die; or 
they may remain latent, as has been suggested, for 
certain lengths of time without producing visible effects, 
and only show symptoms of infection later; but we have 
no experimental confirmation of any such latency ex- 
isting with regard to the tubercle bacillus, and it is not 
to be assumed that it does exist. As to the infection of 
the foetus from the paternal side, where the father has 
tuberculosis of the scrotum or seminal vessels (which 
have been found to be tuberculous in exceptional cases), 
we have no reason to suppose that such can occur. 
There are, however, some grounds for belief that infec- 
tion in this way may take place from husband to wife. 
Thus, Girtner found, as a result of his experiments in 
animals, that a large majority of the guinea-pigs and 
rabbits which were brought together with males whose 
semen contained tubercle bacilli died of primary gen- 
ital tuberculosis; but from the rarity of this affection 
in women and cows it may be assumed that tubercle 
bacilli occur very much less frequently in semen of men 
and cattle than in that of the smaller animals. 
Length of Time Tubercle Bacilli Remain Virulent in 
Sputum. Of considerable importance in studying the 
subject of tubercular infection is the question of the 
