OF LIVING MATTER 65 



Very slight changes in the conditions or influences to which 

 the colloid is exposed lead to changes in its constitution — owing 

 to the ease with which a re-arrangement is brought about among 

 its constituent atoms or elementary molecules. Its very existence, 

 as Graham pointed out, is one of " continual metastasis." 



It is owing to the great size and complexity of the molecules of 

 which they are composed that colloids, in their ordinary state, will 

 not pass through a parchment membrane. Their molecules are 

 too big to be able to get through its pores ; though various saline 

 substances will pass through with the greatest ease, and thus can be 

 easily separated by dialysis from the colloids with which they may 

 have been intermixed. 



But, under the influence of certain re-agents, more especially the 

 digestive juices of the stomach and pancreas, proteids undergo 

 most important msdifications which enable them, like crystalloids, 

 to diffuse through membranes. When thus modified they are 

 known as 'peptones,' and in regard to these bodies Verworn 

 says ': — " It is known that they arise by the hydrolytic cleavage of 

 the original proteid molecule, so that the peptones represent the 

 hydrates of the original proteids. Important conclusions follow 

 from this fact. Since the proteid molecule, which was originally 

 not diffusible on account of its enormous size, is split up in the 

 peptonising process into the peptone molecules, which are much 

 smaller and therefore diffusible, but which have the chemical 

 characteristics of proteids, it follows that the proteid molecule 

 is not simple but polymeric, i.e., it consists of a chain-like com- 

 bination of many similar groups of atoms. In the transition to 

 the peptone condition the proteid molecule is broken up with 

 hydration into these single, similar atomic groups, all of which, 

 however, have the chemical characteristics of proteids, but re- 

 present much smaller molecules." 



Let us look at these compounds now from another point of view. 



Before Wohler announced to the scientific world that he had 

 succeeded in building up an organic compound in his laboratory 

 with the aid of no more mysterious agencies than usually lie 

 at the chemist's disposal, and before the labours of other dis- 

 tinguished chemists had been crowned, with a like success, there 

 was more reason than there is at present for the belief that the 

 forces in living things are altogether peculiar, because it was 



' " General Physiology," Transln. 1899, p. 106. 



5 



