THE CORPUS LUTEUM OF PREGNANCY IN SWINE. 77 



with them were vigorously discussed. Golgi denied the identity of his reticular apparatus 

 with the trophospongium, but Holmgren affirmed it, at least in part. The latter view has 

 taken the ascendant. Ram6n y Cajal believes them to be identical (1908). Cowdry 

 (1912) , from the study of specimens prepared by the methods advocated by both discoverers, 

 points out the great similarity of the two phenomena. 



The functional importance assigned to the reticular apparatus by different authors is 

 varied. It seems well established that the appearances are not artifacts, but are present 

 during life. Some have thought them excretory channels, others circulatory paths for cell 

 juices. Holmgren thinks they are often entered by processes of the connective-tissue cells 

 and that they are the morphological expression of vital processes such as the formation of 

 secretion droplets and the like. According to this view the system of canaliculi is an 

 unstable, constantly changing structure, like any other physiologically active organ, a view 

 which explains the variability of the histological appearance. Most investigators have 

 conceived the reticular apparatus to be a constant component of the cells in which it is 

 found, but von Bergen (1904), who studied the canaliculi in a great variety of cells from 

 many organs, maintains the transitory nature of the structure. This latter opinion is 

 certainly borne out by the study of the lutein cells, as will be shown later. 



Cohn (1903), in a careful paper on the histology of the corpus luteUm, states that he was 

 unable to see the trophospongium in the lutein cell, although he had followed the methods 

 of Holmgren; but Vastarini-Cresi (1904), in a short note, mentions, without describing, 

 certain preparations which he had demonstrated at Naples in 1904. Cesa-Bianchi (1908) 

 describes and figures lutein cells of swine which show appearances resembling the tropho- 

 spongium as observed in other cells. By the Golgi method Riquier (1910) demonstrated 

 an intracellular reticular apparatus in the lutein cells of the cow and, what is very important 

 in connection with the findings to be described in this paper, he showed that the structures 

 undergo marked changes with the advancing age of the cell. 



Now, if we take a well-prepared section of the corpus luteum of a pregnant sow, whose 

 fetuses are perhaps 100 mm. long, and stain it with any strong cytoplasmic stain (Mallory's 

 does excellently), careful study of the lutein cells shows that the cytoplasm contains un- 

 stained areas which are roughly concentric to the nucleus, and which appear to form 

 canal-like paths in the cell (fig. 8). If we take younger corpora lutea, we find the canalic- 

 ular apparatus growing more and more complex. It assumes the form of wide V-shaped 

 spaces, long clefts, and circles in the cytoplasm, so extensive that the nucleus is surrounded 

 by only a narrow zone of endoplasm (fig. 7). But it is in the corpora lutea of pregnancies 

 under 30 mm. that the highest development of the exoplasm is found (figs. 4 and 5). 

 Here the exoplasm is occupied by a most curious and elaborate system of vacuoles, almost 

 every one of which in turn contains a spherule of substance which, although it takes the 

 same stain as the cytoplasm, yet has a more hyaline appearance, and is seen on section as a 

 bright ring. Within many of the spherules is found another and tiny vacuole. 



Curiously enough, the only investigator who has previously described this remarkable 

 state of the lutein cells is F. Cohn (1903), who is mentioned above as denying the existence 

 of the trophospongium in lutein cells. He observed all the appearances which have just 

 been mentioned, in the corpus luteum of the rabbit at the height of its development, and 

 undertook certain microchemical studies on their nature. He found that the innermost 

 tiny vacuole contains a substance which blackens with osmic acid, presumably fat. In the 

 sow's corpus luteum (fig. 6, a) I have been able to confirm this observation of Cohn, but 

 not his other observation, namely, that the outermost vacuole, or clear space about the 



