SYNERi:SIS 101 



tically ins()liil)le in water. The /3 form is very soluble in water. 

 On warniino- some of tlie former willi water it gradually passes 

 into the soluble form and thus goes into solution. Insoluble 

 a partieles may be dispersed in larger particles of j8 + water. 

 They in turn form a true sol with water. Alteration of i)hysical 

 or chemical conditions will therefore alter the relative concen- 

 tration of a and ^. The jS colloid protects its a relative from 

 coagulation by thus forming a pellicle round it. Starch — a 

 pseudo-colloid — is a mixture of several carbohydrates of high 

 molecular weight, each of which is capable of taking up a different 

 quantity of water. (See Emulsions, Chap. IX.) 



A similar difficulty occurs in attempting to explain the colloidal 

 behaviour of some of the proteins. The globulins offer an interest- 

 ing and somewhat bewildering field of study. They are insoluble 

 in Avater, but soluble in neutral salt solutions in the neighbourhood 

 of their isoelectric points. In the list of isoelectric points given on 

 p. 91 you will find that edestin, a vegetable globulin, is given no 

 definite figure, but a range from jjH 4-5-8-0. That is, between 

 those wide limits of hydrogen ion concentration, the reactivity of 

 edestin is at its lowest. Somewhat similar figures could be 

 adduced for the blood globulins. They have large molecules, but 

 very few polar groups capable of combining readily with acid or 

 base — too few indeed to carry them into solution under physio- 

 logical limits of pH. They, therefore, carry the burden of retaining 

 salts, especially sodium chloride, within the body if they are to 

 remain in solution (see Blood). 



It has been shown by Starling that the colloids of the blood were 

 the factors determining the volume of the blood, and that their 

 osmotic pull acting against the filtering force of the blood pressure 

 controlled the output of urine, the formation of lymph, etc. 

 Bayliss clearly demonstrated the function of these colloids, 

 especially in the neat balance between albumin and the globulins 

 in maintaining the viscosity of blood. Swelling of colloidal matter 

 in the erythrocyte under the influence of an acid (COg) plays a large 

 part in securing efficient oxidation in the body, and adsorption is 

 necessary for the life of the cell (p. 134). Further, colloids may be 

 regarded as great reservoirs of energy in the body — 



(1) As colloids have extremely low osmotic pressures they are a. 

 suitable medium for the storage of potential energy. Carboliydrates 

 may be stored as starch or glycogen, both colloids, and changed 

 readily into maltose or glucose, which are crystalloids. 



(2) The salts adsorbed by a colloid are thus rendered osmotically 

 inactive, but may be set free again by alteration of the colloidal 

 electric charge. 



