MULTIPAROUS FEMALES 435 



This type of corpus albicans is found exclusively in lactating females and differs from the more 

 usual corpus albicans, both in its morphology and in its histology. The morphology is similar to that 

 of a corpus luteum of ovulation (Text-fig. 5) ; the mural luteal tissue tends to be thin and usually has 

 a relatively simple folded pattern, and not the very complicated arrangement associated with the 

 full growth and expansion of the corpus luteum. The central connective tissue core is correspondingly 

 simple, and clearly shows its derivation from the original cavity of the collapsed follicle. But the most 

 conspicuous feature is the colouring. This is usually a pale yellow or yellow-buff in colour, as com- 

 pared with the usually darker brown of the majority of the corpora albicantia. In this respect they 

 are similar to the corpora aberrantia which have been described above (p. 380), and which represent 

 former corpora lutea of ovulation. This gross resemblance is confirmed by the histological appearance. 

 The difference between this anomalous type of corpus albicans and normal corpora albicantia is 

 best seen in osmic-treated material (PI. V, fig. 5, cf. PI. V, fig. 6). In normal corpora albicantia 

 the osmic-staining lipoid material is evenly distributed in the hyaline collagen representing the former 

 glandular tissue, and is in granular form. In the anomalous corpora the lipoid material is usually in 

 the form of discrete globules of varying sizes. Where the globules are large the lipoid material occurs 

 at the periphery after fixation, and surrounds a central vacuole which was presumably fluid-filled 



cm 



Text-fig. 46. Morphology of anomalous corpora of lactating females. 



before treatment. There are also lipoid deposits in granular form as in the normal type of corpus 

 albicans, and these granules are more abundant in the peripheral parts of the corpus. The arrange- 

 ment of lipoid material around fluid-filled vacuoles is very similar to the condition of some of the 

 corpora aberrantia and atretica (see PI. VII, figs. 6, 7). 



This similarity between the anomalous corpora albicantia of lactating females and the corpora 

 aberrantia and atretica is suggestive, and it is probable that these anomalous corpora represent 

 ovulations during lactation. The relative age of these corpora (as indicated by the amount of vasculariza- 

 tion for instance) appears to be very similar to the age of normal ' young ' corpora albicantia, from which 

 they differ mainly in the arrangement of the lipoid material. In view of this they do not represent recent 

 ovulations, towards the end of lactation, but probably are the products of post-partum ovulations. 



The mean diameter of nine of these anomalous corpora was 3-8 cm. Considering the small size of 

 the sample, and the fact that the method of measuring may be slightly different, this is quite close to the 

 mean size of the third largest corpus (4-15 cm.) in the sample of lactating females from South Georgia, 

 which on other grounds was assumed to be from a post-partum ovulation. In the period of approxi- 

 mately seven months since its formation it had regressed by 5 1 % in diameter, which was shown to be in 

 close agreement with the rate of regression of the former corpus luteum of pregnancy during lactation. 



About 1 8 % of lactating females are simultaneously pregnant, and of the remaining lactating females 

 about half are presumed (on histological grounds) to have experienced a post-partum ovulation. 

 Combining these data suggests that at least 60% of multiparous females experience a post-partum 

 ovulation. No allowance has been made for the possible variance of these small samples, which is 

 particularly large in respect of the incidence of anomalous corpora. 





