64 



SULPHUR BACTERIA 



water from it were periodically analysed. During this period 

 the pool, which also contained putrescent seaweed, became 

 coloured a deep purple owing to the growth of Thioporphyra. 

 Whilst the chemical changes cannot all be ascribed to Thio- 

 porphyra volutans, the fact that this organism during the period 

 of investigation was far more numerous than any other indi- 

 cates that it was responsible for a very large percentage of 

 the chemical changes that took place. This applies particularly 

 to hydrogen sulphide and the sulphates, which are respectively 

 assimilated and secreted by this organism. 



The following table gives the results of the chemical 

 analyses : — 



The results are represented graphically in Fig. 5. 

 In addition, a total count was made of the saprophytic 

 bacteria, with the followingf results : — 



These tables show that for six weeks the content of hydro- 

 gen sulphide and the number of saprophytic bacteria had 

 steadily increased, the increase in the former obviously result- 

 ing from the increase in the latter. During this period the 



