386 



PROTOPLASM 



readily withdrawn by tapping. The minute (0.5 /j.) globules 

 of rubber remain in suspension and form an ideal material for 

 the observation of the rate of migration in an electric field. In 

 the discussion of emulsions and colloids in general, it was pointed 

 out that the interphase, or that layer which coats the colloidal 

 particle and separates it from the surrounding medium, is the 

 material, or condition, that determines the properties of the 



Fig. 165A. — Mobility curves of latex particles of Euphorbia. {FromL. Moyer.) 



colloidal state. So it is with latex particles; their rate of migra- 

 tion under the influence of an electric field, and their isoelectric 

 point, will be determined not (primarily) by the rubber of which 

 the particles are made but by the protein or other substance that 

 coats them. If the surface layer is protein, it may show the same 

 specificity as to species as do the plant proteins with which Mez 

 worked and the proteins in blood. Moyer first established 

 migration curves, plotting rate of mobility against acidity 

 (Fig. 165.4). The latex when collected is of a fairly constant pH 



