MICROSCOPICAL MEASUREMENTS. 85 



volutions and terminate abruptly in a cul de sac ; in the pan- 

 creas, salivary and mammary glands, etc., they have an arbor- 

 escent arrangement, and terminate in grape-like clusters of cells; 

 the general fact of the distribution of these vessels upon^their 

 walls, and the mode in which secretion is effected being much 

 the same in all. There is no inosculation or direct termination 

 of a blood-vessel in a duct as Ruysch supposed, and the experi- 

 ments that have given rise to this opinion, that of passing a fluid 

 by forcible injection from a secretory duct into a blood-vessel, or 

 vice versa, have been attended by a rupture of the fragile struc- 

 ture of the glands, by which the injection has mechanically in- 

 sinuated itself from one system of vessels into the other. 

 The simplest form of gland, is that of a mere depression or 

 recess in the surface of a membrane, as the sebaceous follicles 

 of the skin or cryptae or follicles of the mucous membrane. 

 These have but a simple orifice, or a short duct. The next 

 degree of complication in the structure of glands, is that of the 

 cellulated or compound follicle, and its highest degree of deve- 

 lopment is met with in the conglomerate glands, as the parotid, 

 the mammary, and the liver. 



Microscopical Measurement of the Diameter of the Capillary 

 Vessels, and Ultimate Divisions of the Excretory Tubes in 

 some of the Glands. 



Parts of an Inch. 



Capillary blood-vessels, according to Weber, - ^ to ^ 

 " " in the kidneys, " Muller, - 2 |g 5 to ^ 

 The smallest pulmonary air-cells in the human sub- 

 ject, (Weber,) which have a termination some- 

 what like the ducts of glands, 5 | 5 to ^ 

 Tubuli uriniferi in the cortical substance of the 



human kidney, (Weber,) ^ 



" " in the pyramidal portion, - ^ 



in the papillae, - $55 



Tubuli seminiferi of man, (Muller,) - T | ? 



" distended with mercury, - ^ 



Tubuli recti testis, (Lauth,) (undistended,) - 



Cells of the Meibomian glands, (Weber,) - 5 |g to ^ 



VOL. ii. 8 



