300 BACTERIA PATHOGENIC TO MAN 



commend itself to all. It is only right to state, however, that up to 

 the present time the actual proof that human tuberculosis has fre- 

 quently come from milk or food infected with bovine tuberculosis is 

 very small, and that it is probable that the bovine bacilli are not as 

 virulent for man as for animals. The relation of bovine to human 

 tubercle bacilli will be discussed more fully later. 



AUTOINFECTION BY SWALLOWING SPUTUM. The secondary forms 

 of tuberculosis which often succeed a primary infection of the lungs 

 may be explained as autoinfections, from the coughing up and swal- 

 lowing of sputum containing bacilli. It is a wonder, indeed, that intes- 

 tinal tuberculosis is not more common than it is in consumption; but 

 this is probably due to the action of the gastric juice and to the fact 

 that in adults the intestines are comparatively insusceptible. 



Hypothesis of Transmissibility of Tubercle Bacilli to the Foetus. There 

 is some evidence of the transmission of tubercle bacilli from the mother 

 to the foetus in animals. The first authentic case recorded is that 

 reported by Johne of an eight-months-old calf foetus; other cases have 

 since been reported. With regard to tuberculosis in the human foetus 

 the evidence is not so clear, though some twenty cases have been reported 

 of tuberculosis in newly born infants, and about a dozen cases are 

 recorded of placental tuberculosis. The fact that statistics show a 

 greater frequency of tuberculous diseases in children during the first 

 than in the following years of life, does not strengthen the hypothesis 

 of frequent infection in utero; for nursing infants would naturally be 

 more exposed to infection through the mother's milk and through 

 personal contact than others. According to experiments upon laboratory 

 animals one would expect to find in man fetal or placental tuberculous 

 infection 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 by Behring and others, 

 for certain lengths of time without producing visible effects, and only 

 show symptoms of infection later; but we have no experimental con- 

 firmation of any such latency existing 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, grounds for belief that infection in this way may 

 take place from husband to wife. Thus, Gartner 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 genital 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. It is believed that the 

 semen of those suffering from advanced or local genital tuberculosis 



