204 STUDIES ON PATHOLOGIC OVA. 



and Dunger that abortive types of hydatiform mole are commonly overlooked," 

 and although he gave no evidence for his opinion, Weber (1892) insisted that 

 hydatiform mole "occurs much oftener than we are led to believe from books 

 or other literature." Essen-Moller says Konig gave an incidence of 1 per 728 

 cases. Pazzi (1908 b ) stated that Dubisay and Jennin found in 1903 that hydati- 

 form degeneration occurs once in 2,000 pregnancies, and that Cortiguera in 1906 

 declared that the frequency of hydatiform mole has a discouraging variation of 

 from 1 in 3,000 to 1 in 700 labors, but that in his personal experience Cortiguera 

 saw one case in every 300 labors. The latter incidence is only slightly higher 

 than that given by Essen-Moller for the clinic at Lund, and somewhat below that 

 of Kroemer (1907), who found 15 hydatiform moles in 3,856 births, or one in every 

 257 cases. Mayer (1911) reported 10 instances among 3,105 cases of labor, an 

 incidence of 1 in 310 cases, and it is only necessary to add that Donskoj (1911) 

 stated that the incidence of hydatiform mole in 28,406 cases at the Frauenklinik 

 at Mlinchen, between the years 1884 and 1910, was only 1 for every 4,058 births, 

 to emphasize the discouraging variation of which Cortiguera spoke. Donskoj 

 also stated that Engel gave the incidence as 1 in 800, and Korn as 1 in 1,250 births. 

 Such a surprising fluctuation in the apparent incidence in adjacent communities 

 points to differences in conception of what constitutes a hydatiform mole, and 

 also to differences in character of the material upon which the calculations are 

 based. 



The existence of hydatiform degeneration in far greater frequency than com- 

 monly supposed is indicated also by the records of the Department of Embryology 

 of the Carnegie Institution of Washington. However, the material covered by 

 these records is not identical with that upon which the above opinions or those of 

 other obstetricians are based. The opinion of the obstetrician is based upon 

 material belonging very largely in the later months of pregnancy, while that in the 

 Carnegie Collection, on the other hand, belongs very largely in the earlier months. 

 Hence this material is not truly representative of the entire period of gestation. 

 But the same thing is true of the material upon which the general practitioner, the 

 obstetrician, and the gynecologists have based their opinions, for these are based 

 largely upon material from the last months of pregnancy. Hence, the cases of 

 hydatiform degeneration which survive mainly come to their attention. 



But unless we can assume that the incidence of hydatiform degeneration is 

 constant during the whole period of gestation, its incidence at any particular time 

 of this period may very incorrectly express that at any other time. This could fail 

 to be true only if the incidence of death of the conceptuses and their susceptibility 

 to hydatiform degeneration were exactly uniform throughout every period of 

 intrauterine life. But we know that neither is true, for it is common knowledge that 

 by far the great majority of the cases of uterine hydatiform degeneration recorded 

 in the literature are mature specimens of total or partial degeneration obtained in 

 the later months of pregnancy. Although such specimens may contain villi in 

 various stages of degeneration, they nevertheless represent end or near-end 



