26 



FREDERICK S. BREED 



But happily the reaction in which we are most interested, 

 reaction 4, can be distinguished from all the others with practi- 

 cally no liability of error. Even supposing a few I's, 2's and 

 3's were to become interchanged, the use of reaction 4 as a 

 quantitative index of development would not be invalidated. 

 The main interest is to discover the ratio of the number of per- 

 fect reactions to the whole number of legitimate pecking reac- 

 tions in the daily series, and to plot the variation of this ratio. 

 The necessary data for this can be gathered with precision. 



2. Data and their significance. The first animals tested 

 were numbers i to 6, inclusive, which will be referred to as 



Tf-ials 



Daya 



2 3 4 5 6 7 8 e 10 11 12 13 14 IS 16 17 18 18 20 21 22 23 24 25 



Figure 1 — The development of the pecking instinct in the chicks of Group A, num- 

 bers 1 to 6, inclusive. Distances along axis of abscissae represent days after 

 hatching; distances along axis of ordinates, the number of a given kind of re- 

 action in a series of twenty pecking reactions. Curve II-A shows the rate of 

 decrease in the daily number of reaction 2; Curve III-A, the same for reaction 3; 

 Curve IV-A shows the improvement in accuracy of reaction 4 for the group. 



Group A. They w^ere hatched on Dec. 2, 1907. Their pecking 

 records cover the period from Dec. 3 to 30, inclusive. Curve 

 IV-A, fig. I, shows the development of reaction 4 for the group. 

 For the calculations only those totals were used in which every 

 chick had a complete series of twenty reactions. Hence a very 

 interesting part of this curve, namely, the detail for the third, 

 fourth, and fifth days, is lacking. The blanks are due to the 

 failure of some of the chicks on each of these days to respond 

 to the food. Improper regulation of the food supply was the 

 cause. Nevertheless, the results were such as to encourage a 

 continuance of the experiment. Barring the vital omissions at 



