No. 647] PROGRESSION OF LIFE IN THE SEA 485 



used entirely as the basis of the culture medium. There 

 was clearly some substance essential to healthy growth 

 contained in the 1 per cent, of natural sea-water, and from 

 further experiments it became practically certain that it 

 was an organic substance. When, for instance, the nat- 

 ural sea- water was evaporated to dryness, .the residue 

 slightly heated and redissolved in distilled water, 1 per 

 cent, of this solution added to the artificial culture me- 

 dium was as potent in producing growth of the diatom 

 as the original natural sea-water had been. When, on 

 the other hand, the residue after evaporation was well 

 roasted at a dull red heat and redissolved in distilled 

 water, the addition of this solution to the artificial culture 

 medium produced no effect and growth did not take place. 

 Growth could also be stimulated by boiling a small frag- 

 ment of green seaweed (Ulva) in the artificial culture 

 medium, the weed being removed before inoculation with 

 the diatom. All this points to the necessity for the pres- 

 ence of some kind, of organic matter in the solution before 

 growth can take place. One must not dogmatize, how- 

 ever, for there are many pitfalls in the experimental 

 work and the necessary degree of accuracy is difficult to 

 attain. My own experience of these difficulties culmi- 

 nated when I discovered, covering the bottom of my stock 

 bottle of distilled water— water which had been carefully 

 redistilled from bichromate of potash and sulphuric acid 

 in all-glass apparatus— a healthy growth of mold. 



Let us then assume that we are allowed to postulate m 

 primitive sea-water or other natural water organic com- 

 pounds formed by the energy of light vibrations from 

 ions present in the water, and see how we may proceed 

 to picture the building up of elementary organisms. 

 Without doubt the evolutionary step is a long and elab- 

 orate one, for even the simplest living organism is al- 

 ready highly complex both in stnu'turo and in function. 

 As the molecules grew more complox by the prou'i'cssi ve 

 linkage of the carbon atoms of newly fonnod carbcliydrato 

 and nitrogenous groups, we must suppose that the or- 

 ganic substance, for purely physical reasons, assumed 



