6 ZOOLOGY 



Chemistry, however, has much to teach us about 

 protoplasm. In chemistry the ultimate particles of 

 the elementary substances are known as atoms (we 

 are not now concerned with the still smaller electrons), 

 and these atoms may be combined in definite systems 

 to form molecules, which are the least possible particles 

 of compounds. Thus water consists of hydrogen and 

 oxygen in chemical combination, the molecules having 

 two atoms of hydrogen to one of oxygen. The water 

 atom is comparatively simple, and is very stable ; that 

 is, it does not readily fall apart, and thus lose its pe- 

 culiar properties. It will be noted that the properties 

 of a compound cannot be readily deduced from the 

 properties of the elements of which it is composed ; 

 thus water has no particular resemblance to oxygen or 

 hydrogen. We are therefore not surprised that the 

 complex compound protoplasm is not like carbon or 

 any of the elementary gases derivable from it on 

 ultimate analysis. 



Protoplasm 3. The protoplasm molecules, composing the smallest 

 system 1 " 6 possible particles of this substance, are known to be 

 of extreme complexity, so that in comparison with the 

 water molecule they are, as it were, richly furnished 

 palaces as compared with a hut. So complex are they, 

 that it has been impossible as yet to construct a formula 

 representing the composition of any one of them, as 

 may be done for most of the molecules known to 

 chemists. With this complexity goes instability, so 

 that protoplasm is constantly in a state of change, the 

 molecules gaining and losing substance. They are 

 therefore dynamic systems of atoms, not static like the 

 water molecule. This power of changing, of being the 

 seat of processes, and therefore the cause of phenomena, 

 is fundamental to life ; but it alone would not suffice. 



