THE FUNCTION OF REISSNER’S FIBER 151 
assuméd earlier. By 4.45 p.m. the tail was lifted more than two inches 
from the floor. The specimen was then driven about the tankand 
compelled to swim actively for several minutes and then removed and 
killed. There was in this case a well marked reaction which endured 
for the entire period of the experiment—53 hours. 
In front of the lesion the fiber has completely withdrawn from the 
piece of terminal filament and spinal cord examined. 
21. The incision was made at 11.40 a.m. August 3. Upon recovery 
from the anaesthetic the specimen adopted the normal attitude. It 
was killed at 10.30 a.m. August 6, having given no apparent reaction 
during the three days of the experiment. 
The sections are poor but show that the incision missed the terminal 
filament and thus failed to break the continuity of the fiber which is 
seen to be of normal diameter and to lie tautly stretched. 
22. Within 10 minutes of the operation (performed at 10 a.m., 
August 4) a marked reaction appeared, the lower border of the caudal 
fin being lifted a clear two inches from the tank floor. The animal 
was sluggish and, after being disturbed, reverted always to this atti- 
tude. It was twice photographed later in the afternoon but the reac- 
tion had then become less marked (figs. 2, 3) but continued as shown 
until the specimen was killed at 5 p.m. Duration of the experiment 
7 hours. 
The fiber has apparently been withdrawn forward from the lesion 
completely beyond the anterior limit of the piece of spinal cord 
sectioned. 
23. The incision was made at 10.10 a.m. August 4, but was followed 
by no apparent reaction and the specimen continued normal until it 
was killed on August 22. It was photographed on August 7 (fig. 6). 
Duration of the experiment 18 days 8 hours. 
The sections show that the cut failed to penetrate the neural canal 
and the normal Reissner’s fiber may be seen lying tautly stretched in 
the central canal of the undamaged terminal filament. 
24. The incision was made at 4 p.m., August 4, and the usual reac- 
tion was noticed within half an hour of the operation, the caudal fin 
being lifted two inches or more. It was, however, less sluggish than 
the subject of the preceding experiment and frustrated all attempts 
to obtain a photograph during the early days of the experiment. The 
reaction continued uninterruptedly until the evening of August 8, 
the photograph (fig. 5) being obtained about midday on August 6. 
From the 9th onwards the reaction appeared intermittently and during 
the whole of the 10th the caudal fin was observed to be resting lightly 
upon the floor of the tank though the head was still somewhat raised. 
Late in the evening of the 15th and again at noon on the 18th the tail 
appeared slightly lifted for a while, but for the most part the reaction 
rarely appeared for any length of time after the morning of the 14th 
August (the eleventh day of the experiment). The specimen was 
notably sluggish during the later stage of the experiment and passed 
most of the time in a corner of the tank, with the tail supported upon 
