M. G. Pavlov's dissertation does not contain particular 

 observations. It is composed of critical reviews of the 

 literature and the author's arguments about the sources of 

 nutrition in the human fetus. This work is interesting 

 because it gives a clear idea about the level of embryological 

 knowledge at that time. The work begins with an address to 

 the Dean of the faculty of medicine of Moscow University, 

 the anatomist E. 0. Mukhin (41), and represents an aphorism: 

 "In arduis audere juvat" (in difficulties it is pleasant to 

 be daring). The dissertation is composed of three chapters, the 

 first of which carries the name "The Appearance and Growth 

 of the Fetus." It starts with a statement that no obstetrician 

 accurately knows how long the time is between conception and 

 the first appearance of the fetus, and, for this reason, 

 there are significant disagreements. Thus, Moriss, Monro, 

 and others have stated that on the third day after conception 

 they have seen in the human ovum an embryo like a worm 

 (vermiculi speciem) . Haller never recognized the fetus before 

 the seventeenth day. The same period is indicated by the 

 "superior and most famous professor, V. M. Richter." (42) 

 Pavlov, here and below, cited the text and drawings of the 

 first edition of Richter' s book, MANUAL OR GUIDE TO THE 

 MIDDLE SKULL (Moscow, 1801). In a short description of 

 the formation of the human fetus, Pavlov to a certain extent 

 follows Richter: "The embryo appears in the form of a dull 

 mucoid cloud, which is swimming in the cleanest fluid of the 

 ovum; it is composed of three vesicles denoting the rudiments 

 of the head, the chest, and the lowest part of the belly" (§ 7). 

 About the third week after conception, in an aborted ovum, 

 it is possible to see a crumpled fetus in the form of a small 

 white body with a small rounded head. It is devoid of all 

 signs of the extremities. It swims on the surface of a 

 completely transparent, colorless fluid, and is connected by 

 means of an umbilical canal with the umbilical sac. In a 

 footnote, Pavlov remarked that specimens of these fetuses, 

 which were obtained by E. 0. Mukhin, were present in the 

 anatomical rooms of Moscow University and the Medical -Surgical 

 Academy. About the fourth week of pregnancy, the body of the 

 fetus looks bloodless, white, and semi-transparent; the head 

 is entirely smooth; on it there is only a small slit denoting 

 mouth formation. The umbilical canal becomes thicker. The 

 rudiments of the extremities appear between the thirty-fifth 

 and fortieth days. During the sixth week, according to Richter, 



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