Infections of the Ovum, Embryo and Fetus 515 



fection has killed the fetus, and it is expelled, the result is 

 known as abortion. If the fetus lives and is carried the full 

 term of gestation and is then expelled, there is metritis pres- 

 ent and perhaps retained afterbirth. The expulsion of the 

 fetus leaves a denuded uterus. If the afterbirth is retained, 

 it is immediately necrotic and decomposes. Then follows 

 an aggravated metritis. It is not a new disease, but a con- 

 tinuation of a metritis which existed during pregnancy, ac- 

 celerated in its course by the uterine denudation of calving 

 or abortion, aggravated by decomposing afterbirth. The 

 infected calf when born may break down with calf scours 

 or pneumonia. It is not usually a new disease or a new in- 

 fection but the continuation of an infection acquired during 

 intra-uterine life. During the course of the dysentery, the 

 alimentary epithelium is damaged or destroyed, permitting 

 the invasion of the body fluids by the bacteria causing the 

 intestinal disease. If the calf suffers from pneumonia, the 

 pulmonary epithelium is damaged or destroyed and bacterial 

 invasion occurs. The infection had its habitat in the 

 pregnant uterus, and thence passed to the digestive tract of 

 the fetus. In the new-born calf apparently the infection 

 passes through the damaged digestive or pulmonary epi- 

 thelium, enters the body fluids, and, having an affinity for 

 the genital tract, regains its habitat there and persists, to 

 interfere later with first pregnancy. According to this con- 

 ception, the infections of which abortion is one significant 

 result constitute an endless chain. They may be intensified 

 in the uterus of the cow just after parturition or abortion 

 and additional infections from the exterior be added. The 

 infection in the new-born calf may be minimized or intensi- 

 fied by proper or improper feeding, or additional infection 

 may be supplied to the calf by association with badly dis- 

 eased calves or by taking milk contaminated by virulent 

 discharges from badly diseased cows. 



On the other hand, the belief that abortion is a specific 

 disease denies the endless infection-chain above described 

 and regards sterility, retained afterbirth, calf scours, and 

 pneumonia as associated or concurrent diseases, but recog- 



