CHAPTER III 

 COLLOIDS AND ADSORPTION 



AS in all biological happenings, the behaviour of 

 colloids and the phenomena of adsorption play a 

 dominant role in the chemistry of micro-organisms. 

 Not only is this true in the actual life processes occurring 

 within the cell and in the action of enzymes isolated from 

 various bacteria, for instance, and bringing about 

 reactions outside the cell, but the colloidal nature of the 

 substances taking part in all the numerous reactions 

 grouped under the heading immunochemistry is obvious. 

 It suffices to mention that all antigens are colloidal and 

 that the antibodies which they provoke are, if not them- 

 selves serum proteins, always carried in the serum and 

 associated with proteins which are colloids. For this 

 reason the properties of colloidal solutions, and particu- 

 larly those of lyophilic colloids, to which class the proteins 

 and complex carbohydrates belong, are of the greatest 

 importance. 



Colloid systems are composed of at least two phases : 

 the disperse phase, consisting of very small particles 

 ranging in size from 10 to 200 m/x (jLt=one micron=one- 

 thousandth of a millimetre and m/x or milli-micron, 

 sometimes erroneously written /x^t, equals one-thousandth 

 of fjL or one-millionth of a millimetre), which are dis- 

 tributed through the dispersion medium or continuous 

 phase. If both continuous and disperse phases are liquids 

 the system is an emulsion ; if a solid is dispersed through- 

 out a liquid the resulting system is known as a suspension. 

 These are the important systems from our point of view, 



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