SECTION ONE 



consist of a meshwork formed by molecular chains of proteins or 

 protein complexes. This outer meshwork would be amphoteric. 

 There would be different degrees of amphotericy, so that some 

 tissue elements would be relatively more basic, and others rela- 

 tively more acidic in reaction. According to Baker (1958), the 

 envelope of the red blood corpuscle is strongly alkaline and one 

 of the least pervious of all tissue elements. 



It is not difficult to imagine this outer meshwork acting as a 

 kind of filter, permitting certain molecules and dye-ions and other 

 ions to pass through its lattices into the inner threshold of the 

 tissue element. Further progress of the molecules and dye-ions, 

 which have passed through this first barrier, would depend upon 

 further obstacles to be met with. Although molecules of slender 

 shape or of low molecular weight may be able to gain entry and 

 perhaps pass along the inner labyrinth of lattices and corridors 

 formed by tissue groups, they may not be able to get out again. 

 They may be trapped by becoming wedged in narrow crevices, 

 or they may be seized by tissue elements of opposite charge and 

 thus held in firm chemical bondage. 



On the acid side of their isoelectric points, proteins exist as 

 cations, and on the basic side they exist as anions. The isoelectric 

 point of a protein (or of a dye) is that pH at which the protein (or 

 the dye) does not migrate in an electric field. 



Acid and basic dyes combine with proteins to form salts and 

 proteinates. The acid dye, eosin, for instance, combines with 

 proteins that are on the acid side of their isoelectric points 

 (protein+ eosin~), whereas the basic dye, methylene blue, com- 

 bines with proteins that are in solution alkaline to their iso- 

 electric points (protein" methylene blue+). Basic dyes, in general, 

 rely upon amino or imino groups or basic nitrogen atoms attached 

 to their aromatic nuclei for their basicity: that is, their power 

 to unite with negatively charged ions of tissues or with other 

 substances such as acid dyes, Carboxylated (acid) dyes rely 

 upon their carboxyl groups for their acidity: that is, their power 

 to unite with positively charged ions of tissues, or with other 

 basic substances. 



Sulphonated dyes rely upon their sulphonic groups for their 

 acidity. When two substances such as a tissue element and a 

 dye unite chemically there is an exchange of ions between 

 the two substances. Proteins already possess basic groups identical 



