We have seen that the voluntary muscles have in general a degree of quickness beyond which they cannot go, and that this quickness belongs to the original constitution. Is not the same phenomenon observed here? Often in two fevers whose symptoms are the same, whose degree of intensity seems to be exactly uniform, the pulse is infinitely more frequent in one individual than in the other. This does not always denote a difference in the disease, but in the primitive constitution, an aptitude of one of the two hearts to contract much quicker under the same stimulant. Who does not know that in experiments, the contractile rapidity is infinitely variable under the influence of the same causes? Each organic muscle has its degree of quickness; the heart, the stomach, the intestines, the bladder, &c. differ remarkably in this respect. III. _Duration of the Contractions._ The heart never remains in permanent contraction, as often happens in the voluntary muscles. Though hunger seems to prove the contrary in the stomach and the intestines, yet this phenomenon is not contradictory; in fact, the permanent contraction of the empty gastric viscera is the result of the contractility of texture. Whenever the sensible organic contractility is in action, there is alternate contraction and dilatation; this alternation even characterizes essentially this last property, and distinguishes it from the animal contractility and from that of texture, in which the state of contraction is often permanent. IV. _State of the Muscle in Contraction._