98 G. F. Firzceratp—On the Superficial Tension of Fluids. 
very thin rings upon one another, a very great pressure might be developed, though 
of course the outer ones would be less effective on account of the greater value of r. 
The case of the heart is somewhat similar to this. 
A constant supply of fresh blood is necessary to keep up the irritability of a muscle, 
because after each contraction the surfaces at which the superficial tension has 
increased have been altered chemically, and it is necessary to remove this debris and 
renew the surface in order to let the muscle relax. We see thus how it happens that a 
contracted muscle requires a constant stimulus to keep it so, and why keeping it con- 
tracted tires the muscle, though no externa! work is performed. For, as there is, 
during life, a continual renewal of the surfaces of the fibrille, there is required a con- 
stant stimulus to keep them as continually changed into the altered state in which 
the superficial tension is increased, while after death rigor mortis sets in, because 
this altered state then becomes the permanent one. 
A remarkable confirmation of my theory is that it completely explains the fact of 
a muscle’s heating when it contracts. Whenever the area of any fluid surface is 
increased it cools, and when it is diminished it heats, and this is true of all Auids yet 
observed, for the superficial tension uniformly diminished when the temperature 
increases, and the law I have just mentioned is a direct consequence of this fact and 
of the laws of Thermodynamics.* Hence, when a muscle contracts, if this be 
accompanied by a diminution of superficial extension, we should expect it to heat, 
- which is what actually takes place. 
In the 58th number of the Quarterly Journal of Science, Dr. Stanley Jevons has 
published a most interesting paper upon what are known as the Brownian motions 
of small particles suspended in a fluid, and attributes them to a very slight chemical 
action producing electrical currents, but he does not explain how the currents pro- 
duce motion. Now, although such'a high authority as Faraday discarded surface 
tension as an explanation of these movements, nevertheless it has been reproposed 
by Tyndal as a possible explanation, and I think the motion of a drop of mercury 
in a horizontal glass tube when an electric current traverses some dilute acid sur- 
rounding the mercury is a very analogous phenomenon, only that the origin of the 
differences of electrical potential in the one case is external to the immersed substance, 
and in the other case, is probably, as Dr. Jevons supposes, due to a very slight chemi- 
eal action of the suspending fluid on the particle. This explanation is rendered 
_ the more probable by Messrs. Ayrton and Perry’s having shown in the Proceedings 
of the Royal Society (loc. cit.) that almost every case of contact of dissimilar substances 
is accompanied by some chemical action. It is of course possible that these very small 
particles may be carried about by the continually moving ultimate molecules of the 
fluid, which are proved to be in constant motion by the phenomena. of diffusion, but 
it is very improbable that such is the fact, though in that case no energy need be ex- 
pended in order to keep up the motion which might consequently go on for ever. Con- 
sidering the very complex chemical constitution of organic substances, it is similarly 
possible that muscular contractions are due to some rearrangement of the ultimate 
molecules constituting the muscle, but in that case it seems improbable that the 
(* See the Theory of Heat, by Professor J. C. Maxwell, in the Text Books of Science Series, p. 291.) 
