4 INTRODUCTORY. 



It is not, however, tlie mere presence of proteids which is 

 characteristic of living matter. White-of-egg (albumen) contains 

 an abundance of a typical proteid and yet is absolutely lifeless. 

 Living matter does not simply contain proteids, but has the 

 power to manufacture them out of other substances; and this is 

 a property of living matter exclusively. 



The waste and repair of living matter are equally character- 

 istic. The living substance continually wastes away by a kind 

 of internal combustion, but continually repairs the waste. More- 

 over, the growth of living tilings is of a characteristic kind, dif- 



o rr> o 



fering absolutely from the so-called growth of lifeless things. 

 Crystals and other lifeless bodies grow, if at all, by accretion , or 



t/ O (/ 



the addition of new particles to the outside. Living matter 

 grows from within by intussusception, or the taking-in of new 

 particles, and fitting them into the interstices between those 

 already present, throughout the whole mass. And, lastly, liv- 

 ing matter not only thus repairs its own waste, but also gives 

 rise by reproduction to new masses of living matter which, 

 becoming detached from the parent mass, enter forthwith upon 

 an independent existence. 



We may perceive how extraordinary these properties are by 

 supposing a locomotive engine to possess like powers : to carry 

 on a process of self -repair in order to compensate for wear ; to 

 grow and increase in size, detaching from itself at intervals 

 pieces of brass or iron endowed with the power of growing up 

 step by step into other locomotives capable of running them- 

 selves, and of reproducing new locomotives in their turn. Pre- 

 cisely these things are done by every living thing, and nothing 

 like them takes place in the lifeless world. 



Huxley has given the best statement extant of the distinctive properties 

 of living matter, as follows : 



" 1. Its chemical composition containing, as it invariably does, one 

 or more forms of a complex compound of carbon, hydrogen, oxygen, and 

 nitrogen, the so-called protein (which has never yet been obtained except 

 as a product of living bodies), united with a large proportion of water, 

 and forming the chief constituent of a substance which, in its primary 

 unmodified state, is known as protoplasm. 



" 2. Its universal disintegration and waste by oxidation, and its con- 

 comitant reintegration by the intussusception of new matter. A process 

 of waste resulting from the decomposition of the molecules of the proto- 



