STAINING, ELECTRON 



stained. However, close inspection of the 

 micrographs of lead nitrate-treated colla- 

 gen reveals that there are numerous small 

 particles adsorbed on the surface and depos- 

 ited in the microcrevices of the fibrils. This 

 type of enhancement of contrast may be 

 termed pseudo-electron staining. There is no 

 chemical combination of collagen with metal 

 in pseudo-staining. 



Figures 1 and 2 compare unstained (i.e., 

 non-treated) and electron stained (phospho- 

 tungstic acid treated) collagen fibrils, re- 

 spectively. Note the greater contrast and 

 enhancement of ultrafine structure in the 

 electron stained material. 



Figures 3 and 4 compare "negative" elec- 

 tron-stained collagen with electron-stained 

 collagen, respectively. In both instances the 

 stain is a chromium complex. The enhanced 

 contrast of the "negative" electron stain is 



Fig. 1. Cowhide collagen fibrils. 31,500X. 



Fig. 2. Cowhide collagen fibrils. 82,600X. Stained 

 with 0.1% phosphotungstic acid (HaPWioO^- 

 24H2O). 



Fig. 3. Cowhide collagen fibrils. 15,400X. 

 Treated with chrome alum (3% KCr (804)2- 

 I2H2O + 10% NaCl) liquor— pH 2.8. Note that the 

 chromium is concentrated along the edges of the 

 fibrils. 



Fig. 4. Cowhide collagen fibrils. 15,400X. Same 

 preparation as in Figure 3 only after neutraliza- 

 tion with sodium bicarbonate to pH 4.5. Note that 

 the chromium is now incorporated in the fibrils. 



Fig. 5. Cowhide collagen fibrils. 15,400X. 

 Treated with lead nitrate (Pb(N03)2). The lead 

 particles are distributed evenly on the surface of 

 the fibrils delineating fine periodic structure both 

 parallel and perpendicular to the fibril axis. 



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