4 GENERAL BIOLOGY 



reproduce themselves, but, as we shall see later, 

 this is but a discontinuous form of growth, and may 

 be paralleled, perhaps, in other " inorganic " bodies. 



Life and Death. If we find it so difficult to 

 point to any one thing as the touchstone of living 

 matter contrasted with non-living matter, what 

 shall we say of the difference between that which is 

 alive and that which has been, but is no longer, in 

 other words between living matter and dead matter ? 

 A turtle may justly be called a dead turtle if we cut 

 off its head, yet, if we cut out the heart of such a 

 decapitated turtle and suspend it on hooks in a 

 moist chamber, wet with a weak solution of common 

 salt, such a heart will go on beating rhythmically for 

 days. So long as it beats we are forced to consider 

 the substance composing it as living matter. 



We must make a distinction, then, between 

 general lije and death, which affects the whole or- 

 ganism and elemental life and death, which affects 

 only the elements or tissues. This distinction is 

 much more apparent in animals than in plants on 

 account of the greater degree of specialization in 

 the former. Ordinarily, decay and disintegration 

 in the tissues promptly follow general death, but 

 experimentally we may avoid this contingency if we 

 exclude bacterial invasion, 1 and such a piece of 

 tissue may be kept passively " alive " f or a consider- 

 able interval of time, regaining its functions when 

 replaced in a living organism. In this way sections 



1 See Chapter IV. 



