DEPARTMENT OF EMBRYOLOGY. 83 



PATHOLOGY OF THE FETUS. 

 Intrauterine Mortality in the Pig. 



In the Year Book for 1921 1 gave an account of Dr. G. W. Corner's observa- 

 tions upon the striking histological alterations that are shown by the uterus 

 during the definite periods of the oestrous cycle. This information has 

 enabled Dr. Corner to test more exactly the condition of uteri bearing 

 abnormal and dead embryos, and whether the failure of these embryos to 

 develop can be attributed to their environment. 



If we are to eliminate the environment as a causal factor, the existence of 

 these functional changes makes it necessary to determine not only whether 

 the uterus is simply free of infection and gross pathological change, but also 

 whether it has reached the particular stage of its histological cycle necessary 

 for implantation and nourishment of the developing ova. 



For the purpose of answering this question, Dr. Corner studied 535 

 pregnancies in the domestic sow at all stages of gestation; in each case the 

 number of ova discharged at the ovulation which led to the pregnancy under 

 consideration was determined by count of the corpora lutea; the number of 

 embryos present and the number missing were ascertained ; abnormal embryos 

 were counted and studied, and as far as possible all abnormalities were cor- 

 related to the histological condition of the uterus and of the corpus luteum. 

 Separating his specimens into three groups, he found that in late pregnancy 

 (151 mm. to term) 28 per cent out of a total of 1,265 ova had failed to develop, 

 and of those that developed nearly 2 per cent were abnormal. In the middle 

 period of pregnancy (41 to 150 mm.), of 1,909 ova about 20 per cent failed to 

 develop, and of those that developed 0.47 per cent were abnormal. In early 

 pregnancy (8 to 40 mm.), of 1,306 ova 20 per cent were already missing, and 

 of those that developed 2.2 per cent were abnormal. The commonest type of 

 abnormality met with in these cases was that due to death and maceration, 

 and in the early stages it resulted in complete disintegration of the embryos 

 and membranes; in the later stages the fetus persisted, but became trans- 

 formed into a mummified mass. In many cases the dead embryos in a single 

 uterus were of widely different dimensions, indicating that death occurred at 

 different stages of pregnancy. Furthermore, the macerated embryos were 

 in most cases much smaller than the normal embryos in the same uteri, 

 indicating long persistence of the macerated specimens in the uterus. It was 

 found that the uterine wall overlying these dead embryos was always normal, 

 both macroscopically and microscopically. Since these specimens cover the 

 whole period of implantation, there is no evidence in the pig that faulty 

 implantation is a cause of embryonic mortality and abnormality, but there is 

 much to indicate that embryos may become abnormal in spite of a uterine 

 environment which, by all the criteria at our present command, is both 

 anatomically and functionally normal. It is of interest to note that about 10 

 per cent of the ova never segment, about 10 per cent degenerate after becom- 

 ing blastocysts, and that 5 to 10 per cent become abnormal during the 

 subsequent course of pregnancy, leaving about 70 per cent that develop into 

 living pigs. 



Faulty Environment and the Human Fetus. 

 The majority of investigators who have studied abnormal embryos have 

 laid stress on environment and faulty implantation as causes of defective 

 development. It is to be remembered, however, that they have worked under 



