524 Diseases of the Genital Orga?is 



when I inoculated her. Her blood still showed a high de- 

 gree of infection when she was eight years old. Clinically 

 she has a high degree of genital infection as shown by a very 

 low rate of reproduction. It appears clear, therefore, that 

 those who hope to control or eradicate abortion through the 

 agency of biologic methods must hope for an artificial im- 

 munity in a chronic infection. 



There is a common belief in a natural immunity against 

 abortion. That is, it is stated that after a cow has aborted 

 once, she is not so liable to abort again. The assertion has 

 been made and remade so often and persistently that by 

 mere repetition it has virtually acquired the force of a 

 fact. But it is perverted fact. The influence of abortion 

 upon future reproduction is well shown in Fig. 175. In 

 this instance eighteen apparently vigorous heifers received 

 abortion bacterins in their first pregnancies in order to test 

 experimentally the power of killed bacteria to prevent abor- 

 tion. The heifers in this herd had for some years averaged 

 about 30 per cent, of observed abortions. The heifers shown 

 upon the chart had been handled, except for the bacterins, 

 the same as prior heifers. As calves they had been grown 

 in an abominable "nursery" under pest-house conditions. 

 Dysentery and pneumonia had been virtually universal. The 

 mortality of calves had been high, but the survivors recov- 

 ered their general health and were apparently perfectly 

 sound. Yet this group of vigorous heifers failed to main- 

 tain its original numbers of fertile females. The losses from 

 infections within the genital tract were so great that the 

 female progeny failed utterly to fill the gaps made by dis- 

 ease. If abortion produces a valuable immunity against fu- 

 ture abortions, this group of heifers should have acquired 

 such immunity and have produced, during the period cov- 

 ered by the chart, a notable excess of healthy females in- 

 stead of the discouraging deficit so clearly shown. 



It is perfectly true that many aborting heifers and cows 

 do not repeat the abortion the following year, or, if re- 

 peated, it is not recorded. When an ordinary grade cow is 

 observed to expel a fetal cadaver, she has usually reached 



