SEXUAL BEHAVIOR OF ALBINO RAT 107 



arrangement and the range of its usefulness is limited wholly to 

 the needs of the problem at hand. 



When the list of categories was satisfactorily arranged and 

 pruned down to workable proportions a number was given to 

 each of the items; this was to be used later as a symbol for that 

 item. Then the categories and the numbers that stood for each 

 were thoroughly memorized and tried out in practice for a short 

 tune upon other animals. With stop-watch in hand the observer 

 recorded chronologically in one column of the record blank the 

 tune of incidence of each activity and in a column beside it the 

 appropriate number to denote the category into which it fell. 

 Obviously the time at which each new act began marked the 

 end of the old act. 



From these records the exact duration of every act during 

 each minute of the twelve-minute period was computed. This 

 gave a record of the type of action, its duration, and its relation 

 to other activities in the twelve-minute period. The table that 

 follows gives the catalogue of activities used, together with a 

 code-form or abbreviation that will be used in the tabular re- 

 ports of the data from the observations. 



The young male rat, whether mature or immature, if thor- 

 oughly tame and cage-adapted, usually loses no time in approach- 

 ing the female when she is introduced into the cage. Almost 

 invariably, in these observations, he was at her side before all 

 her feet were implanted on the floor of the cage. He proceeds 

 in a direct and thoroughgoing manner to explore the female by 

 sniffing and licking, nibbling and nosing her body in various 

 places activities which readily cause the receptive female to 

 betray, by actions easily recognized by the experimenter, her 

 condition of receptivity. Evidence of sexual excitement is mani- 

 fested by the male, as a rule, in the first five or ten minutes after 

 the female is placed in the cage or not at all. Hence for practi- 

 cal purposes, it may be assumed that if the animal under obser- 

 vation does not show signs of excitement during the first five or 

 ten minutes, providing he has thoroughly explored the female 

 during that time, he will not ordinarily show signs in from one- 

 half to one hour or more of observation. This practical rule is 



