24 



found that to folloAv in the methods of the past will, as 

 heretofore, be to invite failure. The qiiestion of, in a 

 measure at least, imitating natural conditions underlies all 

 success. There can be no further question of its necessity, 

 whether with aquatic or terrestrial animals. In regard to 

 the mere question of sj^ace, it has been found with hshes 

 that those which it is impossible to keep in an aquarium of 

 a certain size, will live comfortably in one considerably 

 larger. This has been tested in the cases of a number of 

 species very difficult to keep, and it may be emphatically 

 stated as a principle that as the area or space allotted to 

 animals in captivity increases, the symptoms of depression 

 will decrease and the difficulties in keei)ing them diminish 

 in a like ratio. 



In the question of fishes, the question of the purity of the 

 aquarium is one of the greatest importance. The oxida- 

 tion of metals, the decomjposition of paints, and the gal- 

 vanic action resulting from the use of more than one metal 

 in salt water, are all inimical to success. The further inju- 

 rious effects of the decomposition of organic matter, the 

 food or excreta of fishes, etc., in combination with the 

 first-mentioned elements of injury, still further increase 

 the difficulty. Thus the necessity for purity or freedom 

 from injurious chemical action in tanks or circulatory 

 apparatus is one of the principles upon which success 

 depends. 



It has been satisfactorily demonstrated that an abundance 

 of light, and at least some sunlight, is necessary for the 

 healthy development of aquatic plants. This is ]3rol)ably 

 true of almost all living things. The healthy development 

 of plant-life in its turn has its beneficial eft'ect on the de- 

 velopment of animal life, aside from the direct benefits 

 conferred by the action of sunlight in liberating oxygen. 

 Even where animals live in a state of semi-darkness, con- 

 cealed among stones or plants, the air or the water pene- 

 trating to their homes is revivified by the potent infiuence 



