Physiology and biochemistry in modern medicine . SIOLOGICAL PROCESSES the fluid in which it is dissolved, so that the reaction towards othercolloids and towards electrolytes will vary. One feature of proteins of importance in this connection is that knownas the isoelectric point, at which the protein exists -with a maximum ofelectrically neutral molecules. This point is reached by adding acid toa protein solution. The acid represses the dissociation of the proteinacting as an acid, and therefore diminishes the number of free hydrogenions; and at the same time it combines with the NIL groups an
Physiology and biochemistry in modern medicine . SIOLOGICAL PROCESSES the fluid in which it is dissolved, so that the reaction towards othercolloids and towards electrolytes will vary. One feature of proteins of importance in this connection is that knownas the isoelectric point, at which the protein exists -with a maximum ofelectrically neutral molecules. This point is reached by adding acid toa protein solution. The acid represses the dissociation of the proteinacting as an acid, and therefore diminishes the number of free hydrogenions; and at the same time it combines with the NIL groups and neutral-izes the basic characteristics. The alteration in electric charge thus in-duced alters the water-absorbing powers of the protein and thereforeall of the properties which we have seen to be associated therewith(page 63). SURFACE TENSION Before we consider a very important property of colloids known asadsorption, by means of which they are able to perform many reactionsthat do not conform with the laws of mass action, it will be well to. Fig. 17.—Diagram to illustrate surface tension. The rings A and B inclose soap films inwhich a very fine loop of silk is suspended. In A it is loose but in B. where the film inclosedin the loop has been broken, it is drawn into a circle by the tension of the soap film. (FromBayliss.) say a few words concerning the physical phenomenon upon which thisdepends—namely, surface tension. The creation of this force is dueto the fact that, whereas the molecules within a liquid are subjected toequal forces of attraction on all sides, at the surface these forces act onone side of the molecules only, and therefore tend to pull them causes the surface to pull itself together so as to occupy the leastpossible area, and it is this force which constitutes surface surface behaves as if stretched. There are various simple experi-ments that reveal the presence of surface tension. If a film is made ona loop of wire by dipping i
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