78 THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 



hyaline ring, is stainable with one of the methods for demonstrating myelin, Plessen and 

 Rabinowitz's modification of Weigert's hematoxylin. I have seen the ring-like structures 

 in tissue fixed with formalin, osmic acid, saturated mercuric chloride, Zenker's fluid, and 

 absolute alcohol. Although I have not made an extensive search for these formations in 

 various species, I have looked through a number of specimens prepared for other purposes 

 which chanced to be at hand in the laboratory, and found the ring-like bodies in corpora 

 lutea of the human species, the dog, and the cat. Add to these Cohn's original description 

 in the rabbit, and we have seen the peculiar exoplasmic rings in the corpora lutea of ungu- 

 lates, carnivora, rodents, and primates — surely a general distribution among the higher 

 mammalia. Van der Stricht, in his long paper on secretory appearances in the corpora 

 lutea of bats (1912), does not mention them, but the lutein cells of the bat (as are often 

 those of the cat) are heavily loaded with fatty matter which would obscure the other details 

 of the cytoplasm. 



To avoid making an unproved assumption, in this paper I shall refer to these forma- 

 tions merely as exoplasmic formations, but I think there can be very little doubt that they 

 are really one stage of the canalicular apparatus of Golgi-Holmgren, although granules 

 within the canaliculi have never been described in other cells. In the first place, they can 

 be traced back directly through all transitions from cells containing the classical form of 

 trophospongium (figs. 4 to 10). In the second place, ring-like canaliculi are not new. 

 Cattaneo (1914), in a paper on the canalicular apparatus of ovarian ova, figures appearances 

 not unlike those under discussion, except that he shows no bodies within the canaliculi; and 

 Bensley (1910) has shown very similar spaces in the root-tip cells of the onion. The ring- 

 like structures are so beautiful and so striking that one wonders why they have not been 

 emphasized long ago by some of those who have studied the ovary. Still, they require the 

 best of fixation, and in the usual eosin stain are not as visible, as with Mallory's connective- 

 tissue stain and others which give a strong coloring of the cytoplasm. Yet I think they have 

 been seen before and misunderstood. For instance, J. G. Clark (1898) states that the lutein 

 cells of swine become full of vacuoles and their cytoplasm becomes shrunken, but he was 

 probably actually describing the exoplasmic vacuoles, which we shall see to be evidences of 

 cellular activity, not of senescence. 



There is still another important histological element of the lutein cell to be considered, 

 namely, certain granules of the endoplasmic zone which were described by Cesa-Bianchi in 

 1908. He found, in the perinuclear portions of the cell, a large number of densely packed 

 granules about 1 micron in diameter. To demonstrate them, since the multitude of 

 cytoplasmic structures makes them difficult to see in the living cell, he fixes the tissue in 

 Zenker's fluid or saturated mercuric chloride, sections it in paraffin, and stains with any 

 one of a number of staining combinations, especially hemalum-safranin light green, iron 

 hematoxylin, and Mann's complicated methyl-blue-eosin stain. I have repeated the 

 Zenker safranin light green method, but I find that the granules show up fairly well in 

 formalin tissue stained with hematoxylin and eosin, and very well with Mallory's triple 

 connective-tissue stain; indeed, I had observed them in my preparations before I knew of 

 Cesa-Bianchi's work. In tissue fixed with osmic acid they appear as dark-gray granules 

 against the light-gray endoplasm (fig. 9, c). With Mallory's stain they generally take the 

 orange constituent of the mixture and appear as bright round bodies against a blue-gray 

 background (fig. 7, c) ; but when the sections take the aniline blue ingredient of the stain 

 more strongly— as they sometimes do, with the result that the nucleus becomes blue— it is 

 interesting to note that the endoplasmic granules also stain blue. Cesa-Bianchi's figures, 



