RETARDING INFLUENCE OF CROWDING 129 



excreta and glandular secretions are dissolved. in the surrounding 

 liquid medium and come of necessity into intimate contact with each 

 of the contained animals. Presumably, with chickens we are free 

 from inequalities in food, although in the larger pens some may 

 have fared better and others more poorly, especially in view of the 

 flock organization which Schjelderup-Ebbe (1922) has described. 

 Availability of equal floor space does not insure equality of use, and 

 crowding was probably greater the greater the numbers present. 

 Even so, the significance of these observations is not lessened, and 

 the conclusion of Pearl and Surface may be justified that we are here 

 dealing with physiological effects on the reproductive system pro- 

 duced by physiological effects on the nervous system of the order 

 usually spoken of as "psychological." 



It becomes important to follow the differences in egg production 

 during the course of the year with these pullets housed with dift'erent 

 degrees of crowding. The results of such analyses are published by 

 Pearl and Surface (191 1) and are summarized in Figure 6. The 

 months from November to July are based on the averages of records 

 for 4 years; from July through September on the records of 3 years. 

 October is not included because records for only 2 years were avail- 

 able. 



The data summarized in these graphs show that there is no harm- 

 ful effect from keeping pullets in large and crowded flocks during 

 early winter egg production near the beginning of the laying period. 

 In fact there appears to be a significant advantage accruing from the 

 crowding in the first really cold winter month, December. On the 

 other hand, the 50-bird pens show a distinctly better production 

 than do the other lots in late winter and early spring, about the time 

 of heaviest egg production. This difference does not obtain between 

 the birds kept in lots of 100 and those in lots of 150. The harmful 

 effects of summer crowding on egg production shows plainly when 

 the most crowded pullets are compared with less crowded lots. 

 Overcrowding affects summer egg production in a distinctly ad- 

 verse manner. 



There would thus seem to be three distinct aspects of the effects 

 of crowding on egg production in the domestic fowl. First, in early 



