CULTURING OF AMPHIBIAN EMBRYOS S3 



The amount of water per specimen is not the vital consideration, however. It is the sur- 

 face area that is important, so that in a tank measuring 6 x 1 2 x 24 inches one can place 

 200 tadpoles in water not more than 1 inch in depth. Evaporation from this tank should 

 be compensated for by adding distilled water once each week, but under no conditions 

 should tadpoles be placed in deep water. 



Amphibian embryos can tolerate a wide range of oxygen tension but they are very sensi- 

 tive to anerobic conditions. Artificial aeration is not necessary but it is well to place in 

 the tanks some aquatic plants such as Elodea, Nitella, etc. which will continually add 

 some oxygen to the medium. Anuran larvae seem to require more oxygen than do the 

 Urodele larvae. 



LIGHT 



There is no evidence that light is necessary for normal amphibian development (Rugh, 

 1935). However, since larvae can derive nourishment from algae and they do require 

 oxygen, it is well to provide normal light so that plant food can grow and can provide 

 some of the necessary oxygen. Direct sunlight is not advised because of the heat factor. 



TEMPERATURE 



The temperature tolerance of various forms is given in the section on Temperature. The 

 range of tolerance for the various forms is about 24*-'C. , but the scale is high for some 

 and low for others. The Urodela, for instance, develop better at the lower temperatures 

 while the Anura seem to develop better at the higher temperature levels. 



Within the normal tolerance range it is possible to retard or accelerate the normal rate 

 of development of any of the forms without latering the developmental processes in any 

 way. For instance, one can keep Rana pipiens eggs at 1 5 C. , 20°C. , and 25°C. and have 

 three different stages of development simultaneously, all from the same original batch of 

 fertilized eggs. 



The maximum range for all ainphibian larvae is 0°C. to 40°C. , with the optimum range 

 between 12°C. and 25°C. Most laboratories are kept at between 23 C. and 25°C. which 

 is satisfactory for the Anura but somewhat high for the Urodela. 



BACTERIA AND PARASITES 



The most common infection for adult frogs is Red-Leg. Numerous attempts have been 

 made to control this disease. The best method is to eliminate any infected animals upon 

 receipt; to keep the tanks cool and the animals in running water, and occasionally to treat 

 possibly infected animals with weak KMNO^ solution. Copper lined tanks will reduce the 

 incidence of Red-Leg. Saprolegnia is another infection of high mortality and unknown 

 cure. The symptoms include body swelling or bloating. Infected animals should be de- 

 stroyed immediately and the tank sterilized with permanganate. It is a practice in many 

 laboratories to place several copper pennies in the tanks with the frogs, enough copper 

 ions passing into the water to keep down these infections and yet not enough to be toxic 

 for the adults. (In even minute concentrations, copper, lead, zinc, mercury, and bronze 

 are toxic to enibryos. ) 



Salamanders are sometimes seriously affected by a fungus, Monilia batrachus, which 

 attacks the lips and causes open sores. Frogs and toads seem to be immune. This 

 growth is contagious but if treated early by painting the lips with 2% mercurochrome, the 

 disease may be checked. 



