174 DWIGHT ELMER MIXNICH. 



In the second type of experiment, distilled water and a iM 

 saccharose solution were used as stimuli. In these experiments 

 Syracuse watch glasses were used, each containing a layer of 

 absorbent cotton, which was saturated with the solution to be 

 tested. During the first phase of these experiments the flies were 

 given neither water nor food. They were tested with distilled 

 water until a complete extension of the proboscis was obtained 

 in each of three successive trials. A few animals failed to meet 

 this requirement and were discarded. The remainder were con- 

 sidered as standardized animals, 100 per cent, responsive to 

 distilled water, and were subjected to further experiment. 



Care was exercised in the first two trials with water to prevent 

 the animals from drinking, but at the close of the third trial 

 they were allowed to drink all the water they would. Beginning 

 at this point, therefore, a period of water diet was initiated. 

 Trials with distilled water were continued, each animal being 

 allowed to drink each time it responded. On the average, how- 

 ever, the animals ceased to respond after two administrations. 

 \Yhen no response had been obtained in three successive trials 

 the animals were considered to have become zero per cent, 

 responsive to water, a standardization which proved to be very 

 accurate. The animals on which this experiment was completed 

 were, therefore, selected animals which had successfully met 

 two preliminary tests: (i) They had, after several hours without 

 access to water, become 100 per cent, responsive to water; (2) 

 they had upon administration of water, become o per cent, 

 responsive to this stimulus. Out of 27 flies which had met the 

 first test only 5, 3 Phormias and 2 Lucilias, failed to meet the 

 second test in the time covered by the experiment. 



For purpose of comparison, each time a "no response" to 

 water was obtained, during the period of water diet, the animal 

 was immediately tested with iM saccharose. Following such 

 trials the legs were carefully rinsed in distilled water to prevent 

 contamination in future trials. In the trial with \M saccharose 

 following the third "no response" to water, each animal was 

 allowed to drink all of this solution it would. Some individuals 

 "drank" for only a few seconds while others remained with the 

 proboscis extended for more than a minute. Thus, at this point 



