GENERAL SURVEY AND CONCLUSION 185 
Fatigue.—There is, again, another type where fatigue 
is exhibited. 
The explanation hitherto given of fatigue in animal 
tissues—that it is due to dissimilation or breakdown of 
tissue, complicated by the presence of fatigue-products, 
while recovery is due to assimilation, for which 
material is brought by the blood-supply—has long 
been seen to be inadequate, since the restorative effect 
succeeds a short period of rest even in excised bloodless 
muscle. But that the phenomena of fatigue and recovery 
A P M 
Fic. 113.—Faricur (A) In Muscux, (P) in Puant, (M) In Meran 

were not primarily dependent on dissimilation or assimila- 
tion becomes self-evident when we find exactly similar 
effects produced not only in plants, but also in metals 
(fig. 113). It has been shown, on the other hand, that 
these effects are primarily due to cumulative residual 
strains, and that a brief period of rest, by removing the 
overstrain, removes also the sign of fatigue. 
Staircase effect.—The theory of dissimilation due to 
stimulus reducing the functional activity below par, and 
thus causing fatigue, is directly negatived by what 
is known as the ‘staircase’ effect, where successive 
equal stimuli produce increasing response. We saw an 
