518 INTERNATIONAL OONGRESS OF EDUCATION. 
of the German Opera, probably the best mime dwarf who appeared in 
Siegfried, practised the day through a crackling sound which really was 
made by the mutual friction of the vocal cords. Dr. Clarence E. Rice, 
one of our most expert laryngologists, examined my own vocal cords 
while I produced this sound. He said that the oxyhydrogen gas, which 
we employed, made the cords as distinct as though he held them in his 
hand close to his eyes, and that they were distinctly seen to rub against 
cach other to cause the grating sound. The singing voice is not possible 
antil this rubbing together is stopped and the cords are allowed to 
swing freely. 
The sudden coughing which often follows harsh or unnatural singing 
s due to the friction of the back of the larynx upon the muscle which 
separates it from the spine, not to the cords, unless they are in a state of 
actual disease. Let me close by describing a most wonderful experiment, 
made by Harless, more than sixty years ago. 
At midnight, this time being chosen to avoid disturbing noises, with two 
rained assistants, and employing machinery of his own invention, far 
more complicated than a sewing-machine, with most ingenious devices to 
mark the slightest changes of temperature and smallest divisions of 
weight, he first stretched freshly exsected vocal cords till they were 
torn asunder, thus learning how far he could safely try them. Then, by 
gradually increasing the weights in the exactly graduated scale, he noted 
down the exact added weight which would produce the ascending notes 
of a scale of one octave and a half; now taking a fresh specimen and 
stopping just short of rupture. After one hour and a half of constant 
strain in various severe experiments, he repeated, with the very same speci- 
men, his first experiment, with the amazing result of finding that pre- 
cisely the same weights brought precisely the same tones, with one trifling 
axception, which he thought must be charged to the awkwardness of his 
assistants. 
Now, it is impossible to strain any muscle, during its contraction, 
anywhere near any danger of being torn asunder. Long before that point 
has arrived, the utmost lengthening possible will have been reached. This 
is a strict answer to the mooted question. If one asks how long can a 
muscle be contracted without injury, he asks an entirely different ques- 
con. The vocal muscles will become tired like all others, and it is true 
that exceptional use will make them painful and temporarily weaken 
them. But no case has yet come to my notice where a few days’ rest, or, 
in extreme cases, a fortnight, has not fully restored their natural force.