HOW TO FORM. 17 



animal and vegetable life to the weight of water 

 has not yet been determined, but a small gold fish 

 and two small plants have been recommended for 

 a gallon of water. If we suppose the fish to weigh 

 half an ounce, and the plants the same, this would 

 give us about one proportion of organic matter to 

 one hundred and sixty of water. This may seem 

 a small proportion ; but certainly the greatest part 

 of the evil that I have seen occur to the Aqua- 

 vivarium has resulted from the overcrowding of 

 the plants and animals ; they die as people die in 

 a city, not from treading on each other's heels, but 

 that they consume the air faster than it can be 

 manufactured and conveyed to them. It is on this 

 account that all attempts at keeping large fish fail. 

 According to our calculations, a pike weighing a 

 pound would require a tank containing thirty-two 

 gallons of water, and a forest of weeds to decar- 

 bonize and oxygenate the water. This, then, is the 

 reason why, when large fishes are kept in a small 

 quantity of water, it is necessary that it should be 

 constantly renewed. 



The vessel having been determined on, whether 

 it be a hand-basin or a tank of the largest size, the 

 next thing to be done is to put some soil at the 

 bottom. This is better done before you add the 

 water ; and therefore a few words about the soil. 

 It should be recollected, to begin with, that to 

 water-plants soil is not a matter of so much im- 

 portance as to land-plants : with land-plants soil 

 is everything ; but what soil is to land-plants water 

 is to water-plants. Soil is not, however, a matter 

 of utter indifference ; although many water-plants 

 Jiave no roots by which to anchor to the earth, 

 a large number of them have certain peculia- 

 rities of structure which fit them for growing - 

 better on one kind of bottom than another ; thus 



