14 VETERINARY PHYSIOLOGY 



must manifest themselves on account of the large surfaces 

 exposed. Surface tension is, of course, most easily studied 

 at the surface bounding a fluid and air. At such a 

 surface a skin of increased tension exists. Its condition is 

 modified by many factors, among others by the solutes in the 

 fluid. Inorganic salts generally increase, while organic salts 

 decrease it. The solutes which lower surface tension tend 

 to be more concentrated at the surface, those raising it tend 

 to be less concentrated. 



The amount of concentration at such surfaces is often 

 greater than can be accounted for by the condition of the 

 fluid. A process which has been called adsorption occurs, 

 one substance tending to deposit in large amounts upon the 

 surface of another. This seems to depend mainly upon the 

 electric charge of the two substances, those of opposite 

 charges tending to cling together. This may occur between 

 substances in solution and colloids, or between different 

 colloid particles in a compound sol, and may lead to an 

 increase in the size of the particles and to precipitation. It 

 may also explain the membrane-like covering of many cells. 



It is impossible to analyse such an ever-changing substance 

 as protoplasm, and, although what is left when these chemical 

 changes are stopped can be examined, such analyses give 

 little insight into the essential nature of the living matter. m 



The chief constituents found after the death of protoplasm ^ 

 are the proteins, along with small amounts of fatty substances, 

 carbohydrates, and crystalloids. 



Substances entering into the Colloidal Complex. 



1. Proteins. 



1. Physical Characters.— The Native Proteins — those which 

 may be separated from the residue of living matter — have a 

 white, vellow, or brownish colour when dried. In structure 

 they are usually amorphous, but many have been prepared 

 in a crvstalline condition, and it is probable that all may take 

 a crystalline form. The crystals vary in shape, being usually 

 small and needle-like, but sometimes forming larger rhombic 



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