82 BIOLOGY: GENERAL AND MEDICAL 



bustion. We are, therefore, led to the conclusion that 

 the chemical activities are the source of the energy, and 

 that all vital manifestations are physico-chemical in 

 nature. 



The phenomenal differences between vital and non- 

 vital substance is found in the self-constructive and self- 

 sustaining character of the former. 



As has been shown in a former chapter, there is no 

 evidence that living substance is at present self-existent. 

 All known forms spring from antecedent forms of like 

 kind whose origin is as unknown as the origin of matter 

 and force. But such forms of living matter as are known 

 begin life in a very humble form mere specks of proto- 

 plasm constituting the spores, seeds, or eggs of their 

 parents though endowed with the phenomenal self- 

 sustaining and self-constructive powers. 



Remembering that every activity, being an expendi- 

 ture of energy, results in oxidation, and this in alter- 

 ations in molecular composition, we wonder to see no 

 visible result ensue. The secret of this lies in the wonder- 

 ful power of adjustment by which the molecular disturb- 

 ances are immediately compensated for by internal 

 rearrangements of the molecules. 



If the activities be increased by stimulation, we find 

 that the compensatory readjustments are of limited 

 extent and duration, and the organism soon ceases to re- 

 spond. It is fatigued, or it rests, or it enters a state of 

 vital rigidity. If left to itself for a time, the needed 

 adjustments take place and activities begin again, show- 

 ing that the organism still lives. 



Suppose, however, the stimulation be of such nature 

 as to compel the organism to activities of more prolonged 

 duration, attended with greater oxidation and greater 

 molecular disturbance, and the point is eventually reached 

 when the possibility of internal adjustment ends and re- 

 action to the stimulant ceases not because it is tempo- 

 rarily embarrassed by the necessity for adjustment, but 

 because adjustment has become impossible. The crea- 

 ture then dies. 



