LIFE AND DEATH. 285 



the former as in the normal cell, or are but 

 slightly modified to an extent which does no 

 immediate injury to its life. But we must further 

 assume that the same is also true of the invading 

 protoplasm, and that the Plasmodiophora is also 

 supplied with suitable atom-complexes to build 

 up its protoplasm molecules, as fast as they are 

 shattered and the rejecta burnt off in respiration. 



A step further, and we come to instances of 

 Symbiosis, where the commingled masses of proto- 

 plasm of host and invader continue this har- 

 monious action during life. Clearly there are 

 resemblances between these latter cases and suc- 

 cessful grafts, and between both and successful 

 sexual unions where the resulting embryo-cell 

 gives rises to a vigorous and healthy plant ; and 

 the more these resemblances are examined in the 

 light of what we know of symbiosis the more 

 they support our contention. 



Such considerations as the foregoing suggest, 

 then, that life consists in the regular and pro- 

 gressive building up and breaking down of the 

 complex protoplasm molecules, and is necessarily 

 accompanied by the influx of the indispensable 

 food-elements in certain combinations and atom- 

 complexes for assimilation, and by the combustion 

 of some of the debris of the shattered molecules, 

 which combine with the oxygen in respiration and 

 so afford explosions which raise the temperature 

 and enhance the lability of existing molecules, 

 and act as stimuli to the shattering of further 

 molecules. The results of these rhythmical buildings 



