48 Land and Freshwater Animals 



rotating the slide on a turn-table produces a circular concavity similar to that 

 of the ordinary hollow-ground slide." 



CAGE MANAGEMENT 



In the maintenance of animal cultures the big factors are food, 

 temperature, humidity, and sanitation. 



Feeding and watering. Proper feeding is of first importance in the 

 maintenance of animal cultures. Errors are easily made in both amount 

 and kind of food. The amount should be all that will be completely 

 consumed. Over-feeding is a more common error than under-feeding. 



Watering is often as important as feeding, and he who reads the 

 articles that follow will find many ingenious devices for supplying drink 

 while avoiding fatalities from drowning in the pool. For the larger 

 animals commercial chick-watering and rat-watering devices are avail- 

 able. For smaller ones there is such provision as a wide-mouthed bottle 

 filled with water and closed by placing over its mouth a petri dish lined 

 with a sheet of filter paper, the whole then inverted and set on the 

 cage floor. (See p. 433.) Very small insects are supplied both food 

 and drink from open test tubes of capillary smallness filled with liquid 

 and placed where accessible within the cage. 



Temperature and humidity. For ordinary rearing work accurately 

 stabilized temperature and humidity are rarely needed, since the animals 

 are well inured to a considerable range of both. But there is much need 

 for the exercise of judgment in the location of cages with respect to 

 both these factors. 



Cultures which require a certain uniformity of surrounding tempera- 

 ture may be handled in the following ways if regular temperature control 

 apparatus is not available or is not required. For organisms not re- 

 quiring light an under-ground cave, a subterranean room, or some similar 

 below-ground space may afford a fairly regular temperature throughout 

 the year. For organisms requiring light, culture jars may be placed in 

 another container through which a stream of water from some constant 

 source is running. Such provision is often very satisfactory providing, 

 of course, that the water passing through this improvised jacket is rela- 

 tively uniform and of the desired temperature. Workers in lakeside 

 laboratories may sometimes secure the desired uniform temperature by 

 suspending culture containers on ropes hung from a float or buoy in the 

 deep water of a lake. The temperatures at different depths may be 

 determined in advance by the use of an appropriate recording ther- 

 mometer. Since the deeper waters may change little if at all over the 

 desired period, this method is often a convenient one, and it offers the 

 possibility of selecting temperatures in the vertical temperature gradient. 

 Modern refrigeration with thermostatic control has made possible the 



