36 LECTURES ON BIOLOGY 



tion that there a gradual adaptation has taken place, whilst in 

 the experiments mentioned the organisms were exposed suddenly 

 to extreme pressure. Nevertheless, we are justified in assuming 

 that there exists an upper limit of pressure beyond which life 

 becomes impossible. 



Besides these external conditions of life there are internal 

 conditions of structure and chemical composition of the organic 

 substance. As far as we 'know, all life that exists to-day on this 

 earth is bound to the form of the cell, and to the reciprocal action 

 of protoplasm and nucleus. It may be that in earlier earth- 

 periods there existed organisms which had not yet reached the 

 organization of the cell but were a shapeless mass of plasm, 

 though possessing the function of metabolism and reproduction. 

 This theory has indeed been retained by Haeckel until the 

 present day. Accurate investigations, however, have always 

 demonstrated that these so-called monera already exhibited a 

 differentiation into protoplasm and cell-nucleus. Nucleus and 

 protoplasm must, therefore, according to the present state of 

 knowledge, be regarded as essential to the running of the engine 

 of life. Only where all these external and internal conditions are 

 present life becomes possible. 



As varied as is the structure of organisms, as numerous are 

 the disturbances which are caused by a change of these con- 

 ditions. We have already heard that protoplasm is rich in 

 water. The withdrawal of water renders it hard and tough, 

 and its vital activities become suspended, but are not necessarily 

 destroyed ; for numerous organisms may be gradually called 

 back to life from complete 'dry- coma' by the supply of water. 

 Many cells are able to retain life for many years in such a state 

 of rest. The spores of many species of bacteria, for instance, 

 remain alive up to ten years, and dry-preserved grains of corn 

 germinated even after twenty years. But this rest is not un- 

 limited, as many seem inclined to think. The stories of the 

 germination of wheat taken from Egyptian pyramids where they 

 were said to have rested for more than 5,000 years have been 

 exposed as gross deception. When the native guides saw that 

 the foreign tourists were willing customers for this ' wheat from 

 the Pyramids,' they put this knowledge to a highly remunera- 

 tive use and smuggled into the venerable monuments the ordinary 



