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THE DEVELOPMENT OP THE CORPUS LUTEUM. 189 The Development of the Corpus Luteum: a Review. By Francis H. A. Marshall, ITI.A., D.Sc, Carnegie Fellow, University of Edinburgh. (From the Physiological Laboratory of the University of Edinburgh.) THE present paper is the result of an attempt to collect together and give an account of the literature of the for- mation of the corpus luteuni, during the last ten years, that is, since the publication of Sobotta's first paper on the corpus luteum of the mouse. Of the three original hypotheses pub forward to explain the mode of formation of the corpus luteum, and the origin of the lutein cells, that of Paterson, who regarded the structure as derived from the blood coagulum left in the cavity of the Graafian follicle after its discharge, gained few or no ad- herents among subsequent investigators. The other two theories, those of von Baer and Bischoff, on the other hand, have each received a considerable amount of support. Von Baer supposed the corpus luteum to be a connective-tissue structure, in the formation of which the membrana granulosa or follicular epithelium had no share; while Bischoff con- cluded that the lutein cells were formed by the hypertrophy of the epithelial cells of the undischarged follicle. Among the principal supporters of von Baer's view appear the names of Leuckart, His, Kolliker, Slavjansky, Gegenbaur, Benckiser, Schottlander, and Minot. Those who have adopted the alternative theory of Bischoff include Pfliiger, Waldeyer, Call and Exner, Beigel, and Schulin. 190 FBANOIS H. A. MARSHALL. The first really systematic effort to deal with the question was made by Sobotta, whose eai-liest paper on the subject was published in the ' Anatomischer Auzeiger' in 1895. In the following year the complete paper was issued. These papers describe an investigation on the development of the corpus luteum in the mouse, in which a large series of stages was examined, each of them being collected according to a definite plan, the animals being killed at known intervals after the occurrence of coition, in reference to which the period of ovulation had been previously determined. Sobotta's in- vestigation resulted in confirming Bischoff's view that the lntein cells are the much hypertrophied epithelial cells of the undischarged follicle, the connective-tissue element which forms an anastomosis among the lutein cells being derived from the inner layer of the theca. The theca esterna is described as taking no share in the ingrowth, while the theca interna is stated to become entirely used up in the formation of the interepithelial network. The hypertrophy of the epithelial cells is described as being of the nature of a simple enlargement, unaccompanied by cell division. The cavity of the follicle is said to become eventually filled up by a central plug of connective tissue. The conclusions reached by Sobotta regarding the for- mation of the corpus luteum were subsequently corroborated by him in an investigation on the corpus luteum of the rabbit, the stages of development being also obtained by killing the animals at stated intervals after coition. In 1898 Stratz published descriptions of stages in. the for- mation of the corpus luteum of Tarsius, Tupaia, and So rex; and these agree in all essential particulars with the accounts given by Sobotta. The development of the rabbit's corpus luteum was also studied by Honore, who adopted the same method as that employed by Sobotta. According to Honore the inter- epithelial proliferation of connective tissue is derived in part from the theca externa, and not exclusively from the inner theca, as supposed by Sobotta; while the theca interna is THE DEVELOPMENT OF THE CORPUS LUTEUM. 191 stated to be not entirely exhausted by the ingrowth, some .part remaining to form a layer within the outer theca, after the.full formation of the corpus luteum. Kreis's observations on the young human corpus Inteum likewise support the hypothesis put forward by Bischoff. .Belloy, who investigated the formation of the corpus luteum in the rat and guinea-pig, while regarding the lutein cells as • being derived from the follicular epithelium, describes an active proliferation of these cells soon after the follicle's rupture. No figures are given by Belloy, and it seems possible that he has confused the ingrowing cells of con- nective tissue from the theca interna with the membrana granulosa cells. Bouin, who also investigated the corpus luteum of the ra.t and guinea-pig, reached conclusions similar to those of Belloy. Heape, without entei'ing into a discussion on the origin of the lutein cells, lays some stress on the absence of diyision among these cells in the ovaries of certain monkeys, pointing -out that the enlargement is the result of a simple hyper- trophy. Babl, writing especially on the human corpus luteum, con- cludes that the lutein cells have a double origin, arising both from the membrana granulosa and from the theca interna. A number of investigators, on the other hand, since the publication o£ Sobotta's work, have adopted the theory oi'iginally put forward by von Baer, that the lutein cells arise from the connective-tissue wall, the follicular epithelium being either completely discharged along with the ovum and the greater part of the liquor folliculi, or else being partially discharged and partially degenerating in situ. Among those holding this view are His, Kolliker, and Paladino, who have lately reiterated their former opinions. Von Baer's theory has also received considerable support in recent years from Nagel, who has described the corpus luteum in the human subject as an entirely connective-tissue structure. In this he has been followed by Clark, who worked .on the formation of the corpus luteum in the sow. and in .the 192 FJUNG1S H. A. MARSHALL. human female, and claimed that the result of his investigation had put the matter almost beyond question. Clark's account has been confirmed by Doering, who also worked upon the sow's corpus luteum. Others who have adopted the view that the luteiu cells have a connective-tissue origin are Biihler, Wendeler, and Stockel, who have examined and described developing human corpora lutea. None of these investigators, however, appear to liave given an account of the growing corpus luteum in all stages of development, while in the case of several of the accounts, it is not clear that the structures described were not in reality atretic follicles, that is to say, follicles which had undergone degenerative changes without discharging their ova. On the other hand, the words used in a description by Clark point to the conclusion that this author was dealing with the degenerate epithelial cells of an atretic follicle. It seems not improbable that the young human " corpus luteum" which Doering describes was also an undischarged atretic follicle; while Kolliker's opinion that the corpus luteum is a connective- tissue structure appears to he founded on the assumption that the changes undergone by discharged follicles and retrogressive undischarged or atretic follicles are identical in character. His, and also Biihler, with reference especially to Sobotta's work on the mouse, have remarked that it can scarcely be au accidental circumstance that the accounts given of the development of the corpus luteum in the larger animals and in man are radically different from those described for the smaller species. That the discrepancy between the accounts of various investigators depends upon the size of the animals employed does not seem, on the face of it, a very probable suggestion. It is to be noted further that in the investigations of all these writers who have upheld the connective-tissue theory the ages of the developing corpora lutea were unknown, the material in no case being obtained by Sobotta's method of killing the animals at definite intervals after coition. In 1901 the present writer published a preliminary account THE DEVELOPMENT OF THE CORPOS LUTEUM. 193 of an experimental inquiry upon the formation of the corpus luteum in the sheep. In this inquiry the sheep were killed at stated periods either after coition or after the animals had been observed to undergo oestrus. The relation which was found to exist between the condition of development of the corpus luteum and the leDgth of the interval that was allowed to elapse between cestrus and the killing of the animalj was in itself a strong presumption that ovulation in the sheep occurs normally during oestrus. Thus the approximate age of the young corpus luteum or discharged follicle could in every case be determined. The result of this investigation was to confirm in all essential particulars Bischofi's theory, which had been accepted by Sobotta. The sheep, however, was found to present some differences from the mouse in regard to the mode of formation of the corpus luteum, the connective tissue ingrowth beingderived partly from the theca externa, and not merely from the theca interna, and the follicular epithelium continuing to undergo division after the rupture of the follicle, but with greatly decreased frequency. The former of these two observations is in agreement with Honore's statement in regard to the interepithelial connective tissue in the rabbit. The theca interna was said to become entirely used up in the formation of the connective-tissue ingrowth, this statement agreeing with Sobotta's description, but differing from that of Honore. Two years later the complete account of the development of the corpus luteum in the sheep was published. The description given in these papers is thus completely opposed to His's suggestion that the mode of formation of the corpus luteum in the larger mammals is different from what it is in small animals like the mouse and rabbit, unless, as Sobotta remarks, it was intended to include only the ele- phant and the whale in the former category.
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