Plate 4 



A. Example of a plasma membrane at high resolution showing the ultra- 

 structure of this membrane. Material: Amoeba proteus, Os0 4 fixation. 

 Two dense lines ( ~ 20 A wide) are seen enclosing a third less-dense 

 layer ( /— ' 20 A) to form a sandwich-like surface about 60-70 A thick. 

 For interpretations see Fig. 18, p. 38. 



B. The basement membrane as seen in the plantar skin of the rat. PTA 

 stain. M, basement membrane ; D, desmosome ; /, tuft of desmosomal 

 fibrils (tonofibrils) ; C, cross-sections of dermal collagen fibrils ; m, mito- 

 chondrion. 



C. Section passing through the surface of a nucleus in an epidermal cell 

 of the 12-day-old chick embryo to reveal the " pores," the small circular 

 markings seen at O. PTA stain. 



