158 Mr. H. M. Vernon. The Relations between 



Larvae grown in water purified by this filtration through sand are 

 increased in size some 4'2 per cent., whilst as a rule the percentage 

 of ova reaching the full larval stage is considerably increased. 



On keeping sea water in diffuse light the free ammonia soon begins 

 to 'disappear, owing to the multiplication of the small quantities of 

 algae and diatoms in suspension in the water. Thus, in one instance, 

 after ten days 40 per cent, of the free ammonia had disappeared, and 

 after twenty-five days 92 per cent. ; the albuminoid ammonia had, 

 on the other hand, increased by respectively 28 and 101 per cent. 

 Larvae grown in water thus purified were on an average increased in 

 size by 13*4 per cent. 



On keeping water in direct sunlight for some days, the free 

 ammonia is somewhat diminished, and the albuminoid ammonia 

 considerably increased, probably owing to the formation of vegetable 

 growth. Larvae grown in water which had been exposed four or 

 more days to the sun and air in a covered glass jar were on an 

 average unaffected in size, though only 11 per cent, of the fertilized 

 ova employed reached the larval stage. On the other hand, with 

 water exposed four or five days to the sun in a flask, whereby very 

 little surface was open to the air, nearly the normal number (i.e., 

 66'6 per cent.) of ova developed to larvae, and these larvae were no 

 less than 16*7 per cent, larger than the normal. Bacteriological 

 examination failed to establish any constant differences in the number 

 of germs in these two different kinds of water, but they confirmed 

 the germicidal action of sunlight on the water. It was found, 

 however, that water in which most of the germs had been killed 

 by several days' exposure to sunlight, contained very many more 

 germs than were originally present, if it were subsequently 

 kept in diffuse light. Thus in the subjoined experiment, the 

 water was exposed ten and a half days to direct sunlight, the 

 number of colonies developing after forty-eight hours' incubation 

 being reduced to 70 per c.c. After two days' exposure to diffuse 

 light, however, the number had enormously increased. It will be 

 noticed that the number also increased between the first and fourth 

 days of exposure. This was owing to the fact that there was very 

 little direct sunlight at the time. 



A -"'' ! i / 3 5( >0 



Original water j ^ 



After 1 hour 2,260 



3 hours 1,360 



6 1,450 



3| days 5,500 



7* 150 



10J 70 



12| 320,000 



