12 VETERINARY PHYSIOLOGY 



independent chemical laboratory, separated from others by 

 more or less permeable colloidal walls. 



There is good evidence that when protoplasm is coagu- 

 lated, a marked netted appearance may be observed which 

 may vary greatl}'' in character according to the fixing reagent 

 by which the coagulation has been produced, and which is 

 purel}^ an artifact. 



.III. Chemical and Physical Conditions. 



Protoplasm is not a substance, but a mixture of various 

 substances, a heterogeneous complex, in a constant state of 



flux and change. 



A. WATER. 



Water, holding or held in a Colloidal Complex with certain 

 crystalloids, constitutes something over 75 per cent., and acts 

 as the solvent or suspender of the other materials. 



B. COLLOIDAL COMPLEX. 



The series of substances which constitute the mass of all 

 protoplasm exist in a colloidal state. 



Colloids. 



(1) Colloids were long ago distinguished by Graham 

 from crystalloids by the fact that they do not dialyse 

 through an animal membrane when mixed with water, 

 and he concluded that this is due to the large size of 

 the molecule which constitutes such colloids. More recent 

 investigations have shown that this explanation is insufficient, 

 since substances of small molecular weight may at one time 

 exist in a crystalloid state, and at another in a colloid 

 condition, e.g., silicic acid. 



The essential character of the colloidal state consists in 

 the existence of matter in two conditions, " phases," often so 

 finely subdivided as to render the detection of the con- 

 dition very difficult. The natures of the external or 

 continuous phase and of the internal or dispersed phase 



