106 PHYSICAL CHEMISTRY IN MEDICINE. 



a certain parallelism between changes in colloids and 

 many manifestations of cell life; in the second, however, 

 we are dealing with a direct applicability of the laws of 

 colloid chemistry, controllable at any time by experiment. 

 We will to-day discuss only these last-named phenomena, 

 the importance of which has recently been pushed into 

 the scientific foreground, more especially through the 

 modern development of the teachings of immunity. 



Before attempting an explanation of the significance 

 of the phenomena which interest us especially, it is 

 necessary to obtain a clear conception of the characteristic 

 properties of the colloidal condition. These character- 

 istics are best illustrated by the properties of the colloidal 

 solutions of metals, from which a gradual transition to 

 the biologically important colloids occurs. 



If a clean metal plate, such as platinum, is put into 

 water it assumes a weak electric in this case negative 

 charge, while the fluid surrounding it becomes electro- 

 positive. According to the fruitful conceptions which 

 NERNST has developed of the source of galvanic currents, 

 we have to deal with the following process : Just as after 

 the solution of a salt such as sodium chloride in 

 water the metallic portion is present in the form of 

 electropositive particles, the acid portion in the form of 

 electronegative particles or ions, a metal when dropped 

 into water also goes into solution in traces to form 

 electropositive metallic ions, while the metal itself be- 

 comes a negative electrode. A proper combination of 

 such metals having different solution tensions then con- 

 stitutes a galvanic element. If now we imagine such 

 a metal divided under water into smaller and smaller 

 particles until this metallic dust is able by virtue of its 



