38 FUNDAMENTAL PROPERTIES 



then they come to rest, encysting themselves, and begin rapidly to 

 digest the comparatively enormous mass of food which they have 

 taken — probably by means of some very powerful enzymes foi'med 

 in their interior. Processes of discolourisation go on as in the 

 Amoeba, the food is dissolved, and apparently assimilated as it 

 is dissolved, so that after the expiration of about two days we may 

 see within the cyst perhaps a little pigmentary refuse material 

 which has been cast out, but otherwise only colourless protoplasm 

 in the form of two or four Ciliates, into which the previous single 

 individual has divided. The result is truly amazing, alike from the 

 amount of matter that is disposed of and the rapidity of the meta- 

 bolic processes by the aid of which the vegetable protoplasm 

 becomes animalised. 



(3) We now have to turn our attention to the last of the 

 fundamental characteristics of living matter, namely its power 

 of undergoing processes oi fission, such as those to which reference 

 has just been made, whereby ' reproduction ' in its simplest form 

 is brought about. This mode of reproduction differs little from 

 growth itself ; it was, in fact, long ago aptly termed by Huxley 

 " discontinuous growth." 



In regard to the problem as to the cause of this discontinuity, or 

 what brings about the spontaneous division which is so prone 

 to occur in living units of various kinds, the reader will be in 

 a better position to form some idea after we have briefly dealt 

 in a later chapter with the question of the " Molecular constitution 

 of living matter." It must suffice to say here that it is commonly 

 recognised both by chemists and biologists that protoplasm must 

 be made up of molecules of the most extreme complexity, the con- 

 stituents of which are in a constant state of flux and change, 

 often merely from one isomeric state to another. A condition of 

 unstable equilibrium, in fact, is presumed to exist, constantly 

 varying in response to changes in the medium. And it is assumed 

 that for each of the innumerable different varieties of what we call 

 protoplasm there are, when in this or that medium, certain varying 

 but not very precise limits of size, beyond which the molecular 

 activities of the plastide or cell seem no longer consistent with the 

 existence of only one centre. Two centres, therefore, in some way 

 become established, and the attractive influences associated there- 

 with cause the semi-fluid substance of the protoplasm to gather 

 round each of these centres till ' discontinuity ' is established. The 



