National Geographic : 1954 Nov
terms of, say, hydrogen ion concentration or oxygen balance. One is concerned mainly with setting up an aquatic display that will delight young eyes and provide a healthy and comfortable environment for the fish. A Green Thumb Helps However, as many aquarium enthusiasts will testify, to achieve even these simple ends is not always easy. Keeping fish as pets is more than just adding water, sand, plants, and specimens to a tank. Many a person has watched his aquarium, for mysterious reasons, irreversibly go to seed and become an eyesore rather than an attraction. On the other hand, the fact that so many people, wholly without knowledge of the biochemical principles of the balanced aquar ium, can set up and maintain beautiful and healthy aquariums, is an indication, perhaps, that common sense and a "green thumb" are actually more important than detailed tech nical knowledge.* At any rate, such was the attitude I adopted as the children and I graduated from that first simple goldfish bowl to a series of 2-gal lon aquarium tanks. The first tank had gup pies, perhaps the hardiest of the scores of "tropicals" available for home culture but not necessarily the most elegant. * See "Tropical Toy Fishes," by Ida Mellen, NATIONAL GEOGRAPHIC MAGAZINE, March, 1931. 647 Famous Skyscrapers Flank the Zahls' East River "Zoo" For seven years Dr. Paul A. Zahl, distinguished biolo gist and physiologist, has re sided with his family in the heart of Manhattan. Their apartment, in a 3-story building overlooking Frank lin D. Roosevelt Drive, lies but a few blocks north of United Nations Headquar ters (left) and northeast of the Chrysler and Empire State Buildings (above). The Zahl children, Paul and Eda, have known no other home. The parlor menagerie was conceived by their father to permit the youngsters to study Nature firsthand, an opportunity usually denied city dwellers. From rocking chair and horsy-seat (right) they look on fascinated as father per forms "Operation Siphon."