178 PHYSIOLOGY OF MICROORGANISMS 



substance in the second class, as crystalloid, one and the same substance 

 may exist in both classes. Therefore, two conditions or states of the 

 same substance may be found, the one the colloidal, the other the 

 crystalloidal condition or state. Consequently, substances cannot be 

 divided in accordance with the early views of Thomas Graham, but 

 the conditions or state under which they exist, may be so divided into 

 colloids and crystalloids. The resolution of these classes, as will be 

 seen, is fraught with many difficulties. 



The usual ultimate chemical and physical conception of matter is 

 molecular and atomic. Associated with this are physical properties 

 and qualities. Comparatively recently, matter has taken on new 

 interpretations for the molecule and atom have extended to the electron 

 and sub-electron possessing definite electric potentialities. In the 

 opposite direction there appears to be an aggregating or massing power 

 along with the solvent belonging to the molecule in which the atom and 

 electrons may be active. This aggregating power does not seemingly 

 manifest itself in the same manner with all substances; in other words 

 the particle resulting from this aggregation in the case of hydrated 

 silicic acid may not be executed in the same manner as in the case of 

 ferric hydroxide; in the case of gelatin, as in the case of casein; in the 

 case of particulate gold as in the case of particulate carbon. Such 

 aggregate particles, apparently, are different from the molecular or 

 atomic particles in their structures and reactions and the term aggre- 

 gate does not convey the true structural nature. In molecular reactions 

 chemistry follows its usual course; in the particulate reactions, physical 

 manifestations form the basis of recognition. These differentiations, 

 while helping to distinguish between the well known structures met in 

 crystalloidal chemistry and the more or less amorphous structures of 

 colloidal chemistry cannot be held as a fast cleavage line because they 

 merge into each other and too little is understood of the structure of 

 colloids. They, however, are suggestive, directive and helpful. 



Crystalloids form, as a rule, true molecular or ionic solutions (see 

 Solutions, p. 1 56) while colloids form solutions of a more or less mechani- 

 cal character; the former produce a uniformly dispersed homogeneous 

 system not separable mechanically, the latter give rise to a solution 

 mechanically separable and not uniformly dispersed a heterogeneous 

 system. Also the former give rise to a one-phase system while the 

 latter yield a polyphasic system. The solution of colloids is concretely 



