620 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
(2) the fouling of water by animal life. The experimenter gives a full 
account of his methods, and he thus summarises his results : — 
Green sea-weeds, such as TJlva, rapidly remove the free ammonia from 
aquarium tank water, but they slowly increase the organic ammonia. 
Larvae grown in water thus purified are, as a rule, increased in size. 
When grown in direct contact with the alga, they are generally decreased 
in size, but an increased proportion of the fertilised ova develop to larvae. 
Red sea-weeds, as Gelidium , generally cause an increase in the free 
as well as in the organic ammonia. They sometimes have a favourable, 
but as a rule an unfavourable effect on larval growth. Filtration through 
sand may remove almost all the free ammonia present and a third or 
more of the organic ammonia, this purification being effected by the 
layer of diatoms and algae on the grains of sand. Sand kept in darkness 
may also effect great purification, in this instance through bacterial 
influence. Larvae grown in water thus purified are increased in size 
some 4*2 per cent. 
On keeping water in diffuse light for some weeks, nearly all the free 
ammonia disappears, owing to the multiplication of the small quantity 
of algae and diatoms originally present. The organic ammonia is at the 
same time increased, but larvae grown in the water are greatly increased 
in size. 
Larvae grown in water previously exposed under certain conditions 
to the sun are greatly increased in size. Sunlight, though it has an 
immediate germicidal action on the water, probably effects no bacterio- 
logical purification. 
On keeping water in darkness for three or more weeks, nearly all 
the free, and a third or more of the organic ammonia, is removed by 
bacterial action. Larvae grown in water thus purified are some 7*5 per 
cent, larger than the normal. As far as the ammonia is concerned, water 
kept in darkness may become as pure as open sea-water, but it is not 
physiologically so pure, for larvae grown in the latter are 16 per cent, 
larger than the normal. 
A very considerable purification of the aquarium water is effected by 
the layer of bacterial slime coating the inside of the conducting pipes. 
Thus half of the ammonia was sometimes removed by this means, and 
the larvae grown in the water were 7 * 8 per cent, larger than the normal. 
Larvae grown in water filtered through asbestos and water previously 
heated to 50°, 76°, or 100°, are considerably increased in size, 
t Larvae grown in water previously fouled by fish, crabs, molluscs, and 
Holothurians, are increased in size, but in water fouled by Echinoids 
and other Plutei, are considerably diminished. Dead Echinoids foul 
the water about ten times more than most living animals, whilst fish 
and crabs foul it ten times more than molluscs and Holothurians. 
Ammonium chloride acts very injuriously on larval growth, but 
potassium nitrite and potassium nitrate in small quantities have no 
action. 
Aeration has only a very slightly favourable effect on larval growth. 
The nitrites present are greatly diminished on keeping the water in 
darkness, but are increased by vegetable growth and on development of 
larvae in the water. 
The arm-lengths are, as a rule, affected in the same direction as the 
