68 B. F. KINGSBURY 



easy (Flemming's fluid fixation, the sections bleached and stained 

 with iron hematoxyhn) some few interstitial cells may have been 

 present and not detected. This is easily possible from the mode 

 of their formation. Saimont ('05) has described and figured 

 them as occurring in the basal connective tissue nucleus and in 

 the stromal lamellae between the medullary cords in fetuses of 

 29 to 52 days age (ca.-25 to 91 mm. length). He has recognized 

 in the cat's ovary three periods of development of interstitial 

 cells, (a) the period just referred to; (b) a second period, from 

 about 58 days postcoitum (ca. 120 mm. length) to sixty or sixty- 

 seven days postpartum, in which they occur in the neighbor- 

 hood of the rete and in the zone of the medullary cords; and (c) 

 a third period, extending from about 50 days postpartum into 

 adult life in which they occur as the large thecal cells in follicles 

 in process of development (en voie de developpement) . The 

 interstitial cells of the first period seem to completely disappear 

 before the second period sets in. These cells I have not studied, 

 and hence cannot discuss their mode of origin. The distinction 

 of the second and third periods is one of convenience only. As 

 will appear subsequently my conclusions as to the origin of cells 

 of the 'third period' and the interpretation for all periods are 

 quite the reverse of Saimont's. 



As to the origin of the interstitial cells, the statement of my 

 conclusions is brief. They arise as a modification of stroma 

 cells, and the stroma is therefore the parent tissue for this type 

 of cell. This conclusion is but a confirmation of the results of 

 nearly all later workers upon the subject (Tourneux, Allen, 

 Janosik, and others). 



By increase in the amount of cytoplasm and the appearance 

 of free lipoid therein, the typically spindle shaped stromal cell 

 increases largely in size, and is altered in shape, becoming thus 

 recognizable as an interstitial cell. The correspondingly elon- 

 gated and densely staining nucleus enlarges to a spherical form, 



ployed in this method. The lipoid granules are completely preserved by this 

 technique; (b) fixation in modified Zenker's fluid (1 per cent of acetic, or less), 

 followed by a dichromate mordantage, paraffin imbedding, and a Weigert hema- 

 toxylin stain, as described in the Anatomical Record, vol. 5", p. 313. 



