HYDATIFORM DEGENERATION IN TUBAL AND UTERINE PREGNANCY. 337 



that it may be found but once in 2,400 cases." Williams adds, however, that in his 

 own experience it occurred even more frequently than stated by Williamson; and 

 Essen-Moller (1912), on the basis of 6,000 cases treated between 1899-1908, gives 

 the incidence at the Frauen-Klinik at Lund as 3 per 1,000. My former colleague, 

 De Lee (1915), in commenting on hydatiform degeneration, also stated that he has 

 "frequently found in aborted ova one or more villi degenerate and forming vesi- 

 cles"; and similar remarks were made also by others, notably by Miiller (1847), 

 Marchand (1895), Veit (1899), van der Hoeven (1900), Hiess (and according to him 

 also by von Hecker), Langhans, Weber, and Frankel. Findlay (1917) also regards 

 "it as fair to conclude with Veit, Freund, and Dunger that abortive types of hydati- 

 form 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 3 ) stated that Dubisay and Jennin 

 found in 1903 that hydatiform degeneration occurs once in 2,000 pregnancies, and 

 that Cortiguera in 1906 declared that the frequency of hydatiform mole has a dis- 

 couraging 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 Miinchen, 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 

 Mall 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 mainly the cases 

 of hydatiform degeneration which survive 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 



