The Eelations between Marine Animai and Vegetable Life. 



363 



in the second of the above experiments after 27 days exposure, 

 1\% of the ova developed to larvse, but these larvse were only 

 hA% larger than the normal. These observations serve to prove 

 therefore, that on exposure of the water to diffuse light for some 

 days or v^eeks, a very considerable puritication, as judged by both 

 chemical and pbysiological Standards, is effeeted by the rapid growth 

 and multiplication of the small quantities of vegetable matter in 

 Suspension in the water. 



The Influenae of Bacteria on the Purification of Water. 



a. The Effect of Sunlight. 



In the experiments just described, the water was exposed only 

 to diffuse light. The effeet of exposure to direct sunlight was also 

 determined. In two series of observations, a layer of water about 

 12 cm. in depth was plaeed in a large covered glass jar, whereby a 

 considerable surface of water was exposed to the air. This jar was 

 exposed the whole day to direct sunlight. Analyses of the water 

 from time to time gave the following results. 



In the first experiment, given in the left half of the table, the free 

 ammonia at first increased somewhat in amount, and then decreased, 

 whilst the organic ammonia increased rapidly. In the second ex- 

 periment, the free ammonia at first dimiuished, and then increased 

 in amount, whilst the organic ammonia rapidly increased as before, 

 it being quadrupled after twelve days exposure. In these two series 

 of experiments, the water was exposed to the action of the air, as 

 well as that of the sun. Two other series were made, in which the 

 water was plaeed in a flask filled up to the neck, whereby only a 

 very small surface was exposed. After remuval of a volume of water 



