Fatigue makes the ascent slow, the height less, and the descent slow (Fig. 44).

Exhaustion of the animal has a similar action; and dilute acids applied to the muscle produce the same effect (Fig. 36).

The effect of fatigue is probably due in a considerable measure to the accumulation of acid products of muscular waste.

a

a

b

b

Fig. 43. - Effect of heat and cold. In a the muscle has been artificially warmed, and in b it has been cooled.

When these are washed out by passing a weak solution of chloride of sodium through the vessels of the muscle, or partially removed by kneading, it regains to a great extent its normal power of contraction.

Fig. 44.   Effect of fatigue.

Fig. 44. - Effect of fatigue.

Oxidising agents, such as permanganate of potassium, added to the salt solution, increase its power, and restore the muscle even more quickly and completely.1

Deprivation of blood has a similar action on the muscle to fatigue; and free circulation of blood tends to remove the effects of fatigue.