THE CRITERIA OF LIVINGNESS 89 



cannot operate except under certain conditions, it is an ex- 

 traordinary fact that some creatures can be re-made even 

 after mincing. If a sponge be minced up and forced through 

 a cloth filter, little drops of the debris, placed in appropriate 

 environment, will at once proceed to build themselves up 

 into new sponges. The characteristic metabolism is retained, 

 re-differentiation sets in, the tiny mass begins to feed and 

 grow, the normal organisation is restored, the sponge is once 

 more a going concern. The restoration of the sponge from 

 a drop of debris is as different from the re-building of a 

 crystal from a fragment, as the highly differentiated sponge 

 from the very homogeneous crystal, or as the intensely meta- 

 bolic living sponge from the self-contained, though certainly 

 not inert, crystal. 



(4) If living implies persistent metabolism, we must 

 admit a saving-clause to the effect that the metabolism may 

 sink at times to a minimum. Further investigation will 

 make things clearer, but there is difficulty at present in 

 regard to the familiar facts that dried seeds may retain their 

 power of germinating for as long as a man lives, or that 

 desiccated animals and germs of animals (as in the case 

 of some thread-worms, rotifers, bear-animalcules, and small 

 crustaceans) may remain in a state of so-called suspended 

 animation for, it may be, a dozen years. Small Nematode 

 worms have been known to revive after being fourteen years 

 dry alive rather than living. It has not been satisfactorily 

 proved that mummy wheat germinates, but Becquerel got 

 seedlings from seeds which had lain for eighty-seven years 

 in a herbarium a hortus siccus indeed. 



Becquerel took seeds of wheat, mustard, and lucerne, and 

 perforated their air-tight seed coats ; dried them in a vacuum 

 at 40 C. for six months; sealed them up in an almost ex- 



