Further Studies on the Nephron Ultrastrueture in Mouse 



Fig. 2. Basal part of a cell from the terminal part of proximal convolution. Towards the basement membrane (BM) is seen 

 the plasma membrane without infoldings, in places with a high density of the adjacent cytoplasm. Mitochondria (M) of 

 round or oval shape. Some a-cytomembranes (arrow) with attached 160 A thick granules. Parts of Golgi apparatus (G) 

 and nucleus (N) are seen. Magnification 30,000. 



does not seem probable that the tubular invagina- 

 tions develop into vacuoles, which makes the sug- 

 gestion by Pease (2) seem doubtful. 



The cytoplasm of the cells from the terminal 

 part contains 160 A large granules arranged 

 either singly, or in aggregations of 4-6. The granules 

 are more scarce than in the first part of the proximal 

 convolution, which gives the cytoplasm of the termi- 

 nal part a less dense appearance. The granules have 

 not been found in the brush border extensions, as 

 claimed by Pease (2). There may be a difference 

 between mouse and rat. Several high resolution 

 electron micrographs of brush border extensions from 

 the first part of the proximal convolution have been 

 published (3), where no granules are to be seen. 

 These findings indicate that the cytoplasm of the 

 brush border differs markedly from that of the rest 

 of the cell. This structural difference may be related 

 to functional differentiation of the cells. In very rare 

 cases short a-cytomembranes (6) with the typical 

 attached 160 A granules occur in the cytoplasm. 

 Occasionally, these may also be encountered in 

 the cells of the first part of the proximal convolu- 

 tion of the mouse kidney. 



This study of the mouse nephron has made it 



possible to correlate light and electron micro- 

 scopic findings as far as the lumen of the terminal 

 part of the proximal convolution is concerned. In 

 both cases a wide lumen has been demonstrated, 

 although two difterent methods of fixation were 

 used. The question of a free lumen in the first part 

 of the proximal convolution is not yet settled b> the 

 statement of Pease (2) that a variation in cellular 

 water content is responsible for the presence or 

 absence of a free lumen. Of course, the present author 

 does not deny that a free lumen exists //; vivo, but 

 after fixation with both osmium tctroxide b\ immer- 

 sion and by freeze-drying the lumina of the proximal 

 convolution are aKva\s found to be closed, in con- 

 tradistinction to this, using the same fixation meth- 

 ods, the lumina of the terminal part of the proximal 

 convolution are found to be open. 



According to Pease (2), a "hydration" of the tu- 

 bule cells is responsible for the closing of the lumen 

 when the common fixation technique of immersion 

 is used. He believes that the cells "pick up" water 

 and that they then should be regarded as "swollen" 

 cells. However, if this be true, it seems likely that 

 the density of the cytoplasm of a swollen cell should 

 be less than that of a non swtillen cell. Still, in our 



