2. The intramuscular osmotic pressure may reach, or even exceed, 2.5 atmospheres, or 2.6 kilogrammes per square centimetre of surface.
3. When a muscle is made to contract once a second, the
elevation of the osmotic pressure increases with the number of contractions.
4. The intramuscular osmotic pressure increases with the work done by the muscle.
5. Fatigue is caused by the increase of osmotic pressure in a contracting muscle.
(a) Monopolar field of diffusion. A drop of blood in a saline solution of higher concentration.
(b) Bipolar field of diffusion. Two poles of opposite signs. On the right a grain of salt forming a hypertonic pole of concentration, on the left a drop of blood forming a hypotonic pole of dilution.
The Field of Diffusion.—Just as Faraday introduced the conception of a field of magnetic force and a field of electric force to explain magnetic and electrical phenomena, so we may elucidate the phenomena of diffusion by the conception of a field of diffusion, with centres or poles of diffusive force. If we consider a solution as a field of diffusion, any point where the concentration is greater than that of the rest may be considered as a centre of force, attractive for the molecules of water, and repulsive for the molecules of the solute. In the same way any point of less concentration may be regarded as a centre of attraction for the molecules of the solute, and a centre of repulsion for the molecules of water.
A field of diffusion may be monopolar or bipolar. A bipolar field has a hypertonic pole or centre of concentration, and a hypotonic pole or centre of dilution. By analogy with the magnetic and electric fields we may designate the hypertonic pole as the positive pole of diffusion, and the hypotonic as the negative pole.