48 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



After soaking for two days, bubbles of gas began to rise to the surface of the 

 v\ ater, but no attempt was made to analyze it. The bottom yellowish layer had become 

 80 dense that no object could be seen across it — a thickness of fifteen inches. Its upper 

 surface was sharply marked off from the overlying transparent water by a thin gray- 

 ish layer. Microscopic examination of this layer showed it to be swarming with 

 bacteria. 



For the information of the general reader it may be explained that bacteria are 

 divided into two classes in relation to oxygen. One class can live only when in con- 

 tact with air (oxygen). These are known as aerobic bacteria. The other class can live 

 only in media from which air (oxygen) is excluded. These are kown as anaerobic 

 bacteria. The anaerobic were present at the bottom of the aquarium, the aerobic, 

 chiefly towards the top. But between these two, were to be found other bacteria 

 which could live and multiply either in the presence or absence of oxygen. 



At the end of the week, the water^ especially that siphoned off from the bottom, 

 emitted a sweetish aromatic smell. Only about an inch at the bottom had retained 

 the original yellow colour; the next inch had changed to a yellowish brown; then 

 came a grayish layer about one-sixteenth of an inch thick; above this, what had at 

 first been fourteen inches of perfectly clear water had turned to a dark gray, though 

 still quite transparent. Black bass fry placed in the aquarium at this time at first 

 darted to the bottom, but after meeting the poisonous extract once or twice could not 

 subsequently be driven into it. On the contrary they swam along the top with their 

 nose just touching the surface of the water, and behaved as if suffering from lack of 

 air. They lived only about two hours. 



Four days after this, black bass fry lived only an hour when placed in the upper 

 14 inches of water. That they were suffocating was proved by the fact that, on aerat- 

 ing the water, the fry lived in it for 24 hours, and were then apparently well. 



In three weeks the upper 14 inches of water had changed to a steel gray colour. 



In five weeks the pleasant aromatic odour had given place to a musty disagreeable 

 smell. The laboratory windows being open, mosquito larvse became numerous in the 

 aquarium and appeared to be feeding upon the bacteria which were very abundant on 

 the surface of the bag, and along the sides of the aquarium. 



On July 31, some of the water was siphoned off from the middle of the aquarium 

 and placed outside the laboratory in direct sunlight. Dr. W. T. Connell, Professor of 

 Bacteriology in the University, examined this water on three successive occasions, and 

 compared its bacterial life with that in the aquarium. He found that sunlight and 

 air had killed off those kinds of bacteria which flourish in shade and in absence of 

 oxygen, and stimulated the growth of other kinds of bacteria which flourish in sun- 

 shine and moving water. In a fortnight, this water had become odourless, transparent 

 and brownish in colour. Minnows were able to live in it, and soon played havoc with 

 tile mosquito larvse. 



The water in the aquarium remained slate-coloured, slimy and foul-smelling for 

 two months longer, when it was thrown out. 



SAWDUST BEDS. 



No one needs to be told that sawdust undergoing decay in the laboratory and saw- 

 dust decaying along the beds of rivers and streams must present different phenomena. 

 In the laboratory experiment, the sawdust is always under water, the water is stag- 

 nant, and both sawdust and water are in the shade. Along a stream, sawdust beds are, 

 in spring and early summer, formed under water; late in the season, they are fre- 

 quently exposed high and dry to the influences of sunshine, shade and wind. Only 

 in shady pools remaining after the spring freshets, could the conditions in decaying 

 sawdust approximate to those in my laboratory experiment. Moreover, there is con- 

 tinually passing over all sawdust beds a slow current of water, which profoundly in- 

 fluences the changes going on in decomposing matter. The running water is slowly 

 and surely extracting the soluble organic matter from the wood cells. Day after day 



