168 WALTER LOUIS HAHN. 



not used until the next day. The normal, uninjured animals 

 were liberated in the room and their movements carefully watched. 

 Each time one of them passed between the wires or approached 

 quite near to a wire and appeared to dodge it was called a trial. 

 It was at first intended to allow lOO trials for each bat but it was 

 found that the animals were apt to become tired and refuse to 

 fly before the experiment was concluded and the number of trials 

 was reduced to 50 for each condition. The wings brushing 

 against the wires, even very lightly, produce an audible sound 

 so that it was easy to tell when the animal struck the wires. 



Most of the normal bats flew about the room rapidly for a time 

 and then began to stop frequently, alighting on the walls, the 

 underside of the roof or objects in the room. After a period of 

 varying length some of them attempted to settle down and it was 

 difficult to keep them on the wing. On being driven from their 

 perch they would make short flights only, and stop again. For 

 reasons previously stated (p. 167) striking objects other than the 

 wires were disregarded. 



Four kinds of mutilation were employed: (i) The eyes were 

 covered with an opaque mixture of lamp black and glue. (2) 

 The external ears and tragi were excised close to the head. 

 (3) The external auditory meatus was stopped with a small 

 quantity of plaster of Paris which was allowed to harden before 

 the bat was liberated. (4) The hairs of the body and membranes 

 were pasted down with thick vaseline. 



When the eyes were covered with the mixture of lamp black 

 and glue, the most noticeable effect was to decrease the activity 

 of the animal. Usually a bat so treated alights somewhere and 

 tries to remove the substance from its eyes, using the hind foot, 

 as the thumb and wrist cannot be brought into contact with the 

 head. If the glue is allowed to harden somewhat before the 

 animal is liberated, it is not so easily removed ; even then it is 

 necessary to dislodge the bat as soon as it alights or it will finally 

 succeed in removing the hardened glue. In every instance the 

 animals were examined at the conclusion of the experiment to 

 see that the covering was intact. 



The 47 bats used in these experiments struck the wires 25 per 

 cent, of the 2,350 trials recorded for the uninjured condition. 



