6lO V. T. NACHMIAS AND J. M. MARSHALL, JR. 



the particles are held in a layer about looo Angstroms thick just outside 

 the cell membrane, which is not itself stained by osmium. 



Figure 3, again of a specimen treated with ferritin, shows the effect of 

 2 min. of washing at pH 6-5. Most of the ferritin has disappeared. Longer 

 washing (for 3 to 4 min.) completely removed the protein. In this instance 

 the layer which binds protein is seen as a faintly osmiophilic, fibrillar 

 substance [15]. Usually this substance, the mucous coat, is not well 

 stained by osmium. Its fibrillar character is variable, and may well be an 

 artifact of fixation. 









Fig. 5. Binding of methylated ferritin persists after washing at pH 6-4 for 

 5 to 10 min. 



Figure 4 is a micrograph of a specimen treated with methyl ferritin at 

 pH 4, and washed at the same pH. The binding persists, whether the 

 specimen is washed at pH 4 or pH 6-4 (Fig. 5). 



These comparative studies demonstrated that binding depends upon 

 the net charge carried by the protein, but gave no direct information about 

 the chemical nature of the mucous coat. By working with mass cultures of 

 Chaos chaos in 10 to 50 g. lots, it has been possible to isolate, after tryptic 

 digestion, an acidic, metachromatic polysaccharide. A preliminary analysis 

 suggests that it is a sulphated polyglucose, but this must be confirmed by 

 further investigation. 



