PUTRID WATER. 149 



with using a syringe every now and then, just to 

 mechanically entangle air in the injected water. There 

 is no harm whatever in this method, but we prefer the 

 above fountain. In the huge tanks of our public 

 aquaria the sea water is aerated entirely by various 

 mechanical processes, which will be shortly described. 



Fig. 109. 



Small Wrack (Fticris canaliculatus). a, Spore-case. 



No paint should be used, in the interior, at any rate, 

 of any aquarium; and if it can be avoided on -the 

 outside it is all the better, as the presence of paint 

 seems to cause annoyance and sickness to all kinds of 

 animals. When the sea water becomes putrid it is for 

 want of oxygenation ; and a little artificial oxygen 



