90 



NINTH LECTURE. 



other ; in somewhat larger ones an alternating position begins 

 to take place. 



If, however, we force a stream of dilute nitrate of silver 

 solution through our capillary, it then appears to be com- 

 posed of the plates and curved, nucleated, endothelial or vas- 

 cular cells represented in Fig. 21. With stronger magni- 

 fying powers (Fig. 87), one recognizes in places, between the 



Fig. 86. — 1, capillary with a thin wall, and the 

 nuclei a and b ; 2, capillary with double contoured 

 walls ; 3, small artery, with the endothelial layer a, 

 and the middle layer b. 



Fig. 87. — Capillary from the mes- 

 entery of th< frog \t a and b, small 

 apertures, '"Stomata." 



endo" elia, larger and smaller, mostly rounded, dark cor- 

 puscles (a, a) or light circular markings (b). There are small 

 openings here, through which the lymphoid cells, by their 

 vital migration (p. 10), probably make an active exit, and the 

 colored elements of the blood are passively forced out (p. 27). 

 The former marvellous emigration has been known for years 

 (A. Waller, Cohnheim). 



In other capillaries (Fig. 86, 2) the walls are circumscribed 

 by a double line. Here, there already appears to be the pri- 

 mary rudiments of a so-called tunica interna or serosa. 



