STRUCTURE OF THE EXCRETORY DUCTS. 431 



the lumen of the tube, are united into a highly refractile con- 

 tinuous layer, the cells being here intimately adherent. They 

 are, however, strongly adherent elsewhere to so great an ex- 

 tent, indeed, that when in the fresh condition it is impossible 

 to isolate them. If the surface of the tube be examined, a 

 beautiful mosaic of cells comes into view, the transverse section 

 of the cells being for the most part completely filled by a well- 

 defined nucleus. The cell contents, when a freshly made 

 transverse section of the salivary duct of a dog is examined, 

 appears to be perfectly hyaline. This animal is well adapted 

 for the purpose, because the toughness of the gland (submaxil- 

 lary) permits fine sections to be made of it whilst still warm, after 

 removal from the body. The most remarkable feature of these 

 cylindrical epithelial cells is presented by the surface turned 

 from the canal, and which is immediately in contact with the 

 membrana propria. From this spring a large number of ex- 

 tremely fine varicose hairs, quite a bunch or pencil of such 

 hairs proceeding from each cell. The surface of the tube 

 composed of these cylindrical cells, always easily capable of de- 

 tachment from the membrana propria, appears, on account of 

 the equality in length of the several hairs, like a thick brush. 

 These extraordinarily fine fibrils may be observed in any of 

 the fluids in which the fresh gland can be properly examined. 

 There may also be constantly seen, on focussing the surface of 

 the salivary duct, fine points, which represent the optic trans- 

 verse section of these varicose fibrils. For these reasons I am 

 not disposed to regard these brushes as artificial products, which 

 have originated by a splitting of the peripheric portion of the 

 cells. 



Whilst in most cells the fibres commence immediately below 

 the nucleus, it may be observed in some preparations, in which 

 the cells have been isolated in iodized serum, that a few fibrils 

 take origin from a higher point in the interior of the cell. In 

 many of these cylinders the body of the cell very constantly 

 presents the appearance of being delicately transversely striated. 

 In the greater number of instances, however, that portion of 

 the cell which is next to the canal remains transparent. From 

 preparations made with iodized serum, it can be shown that 

 some of these cylindrical cells, in consequence of the smallness 



