Chap, i ] CHARACTERS OF LIVING MATTER. 3 



diminishes, until at last it dies. From this dead 

 matter, living material can never, by any process now- 

 known to us, be produced ; for, so far as we know, 

 living matter can only proceed from other living 

 matter. 



As the chemist is only able to acquire definite in- 

 formation with regard to the chemical composition of 

 living matter by the use of certain treatments which 

 deprive it of life, we cannot speak with certainty of 

 more than the broad outlines of its composition ; but 

 this, at least, may be said : in living matter (proto- 

 plasm), the four chemical elements, oxygen, hydro- 

 gen, nitrogen, and carbon, are always found, and with 

 them there would seem also to be associated small 

 quantities of sulphur and phosphorus. It is possible, 

 if not certain, that protoplasm is a compound of a 

 number of the so-called proteid bodies, and it is quite 

 certain that what chemists call its " atomic composi- 

 tion " is very high. One of the most complex bodies 

 known to us is that constituent of the brain which is 

 called protagon ; and its " atomic composition " has 

 been determined to be C^B^NgPO^, or no less than 

 509 atoms. When such a body is active, fresh chemi- 

 cal changes are always taking place within it ; it is in 

 a condition of unstable equilibrium; the result of 

 such change, so far as it aftects the living matter, is 

 loss or waste ; in addition to this, living matter is 

 always taking up fresh oxygen, and forming carbonic 

 acid, of which it has to free itself. These activities 

 combined require, as may be supposed, the addition 

 of fresh material from without; that is to say, living 

 matter demands food. The food so taken in may or 

 may not be similar in composition to the organism 

 itself ; but, as the living creature has wasted through 

 all its parts, the fresh material has not merely to be 

 taken in, it has also to be assimilated. When a crystal, 

 placed in a solution of its own material, grows, it does 



