GENETIC TYPE AND THE EXDOCRINES 531 



under identical conditions, and they then classified themselves. 

 By this plan a more natural means of segregation was evolved. 



The experimental situation and equipment. The laboratory 

 in which the experiments were conducted is relatively free 

 from extraneous disturbance. It is situated in a basement 

 with concrete walls, floor, and ceiling, and, as an added pro- 

 tection from accessory stimulation, the animal room was en- 

 closed by a double celotex wall containing a dead air space 

 between the partitions. Figure 1 of plate 99 shows the two 

 rooms of the laboratory. An observation window of two 

 plates of heavy glass was placed in the wall between the 

 animal room and the experimental room. All communication 

 between the rooms was made electrically or by means of 

 quiet mechanical apparatus. The movements of the dogs were 

 recorded by light strings running from the head and leg of 

 the animal to recording levers on a kymograph. These re- 

 cording strings passed from the animal room to the experi- 

 mental room by means of small copper tubing. 



During the experiments the animal was confined by a har- 

 ness to the platform of a food table. On this table w r as a 

 revolving aluminum disk 26 inches in diameter, and six 

 pans were placed equal distances apart on the disk. As figure 

 2 (pi. 99) shows, the table is surrounded by a frame so that 

 only one pan is visible to the dog at any one time. The disk 

 is rotated by a pull on a rope around the axis and is stopped 

 by a rubber cushioned brake which is released by a wire like 

 the choke control on an automobile. One empty pan is before 

 the dog at the beginning of the experiment, and five pans of 

 food may be presented without entering the animal room. 



The apparatus employed to measure the saliva is a modifica- 

 tion of that used by Pavlov. The Lashley cup, consisting of 

 two chambers, one for collecting saliva and the other for 

 maintaining a negative pressure to hold the cup over the 

 parotid fistula, has proved satisfactory. A small rubber tube 

 runs from the inner or saliva chamber to a manometer in 

 the experimental room. The manometer is a 1 millimeter 

 tube graduated in hundredths of a cubic centimeter, and the 



