2o2 A Manual of Veterinary Physiology. 



3-. A muscle at its first contraction can lift its greatest 

 weight ; but as the contraction continues, the weight it can 

 lift becomes less and less. 



During progression the entire strain of the body comes 

 on the feet and the muscles of the limbs, and duriug such 

 paces as galloping the strain is enormous. By galloping 

 a horse over a weigh-bridge, I have observed that a weight 

 equivalent to that of the whole body is imposed on one fore- 

 leg ; it is very easy, therefore, to understand why horses 

 break down, for as their muscles become fatigued they lose 

 their elasticity, and the strain is now thrown on the flexor 

 tendons, which possessing but little, if any, elasticity, give 

 way under the weight. 



Rigor Mortis. — After death a muscle passes into the con- 

 dition of rigor or stiffening, by which it changes both in 

 its physical and chemical aspect. The muscle becomes 

 firm and solid, loses its elasticity, and no longer responds 

 to electrical stimuli ; further, it loses its alkaline reaction, 

 and in course of time becomes acid, due to the formation 

 of lactic and other acids. Through the death of the muscle 

 the fluid myosin becomes coagulated ; it is this coagulation 

 which produces the stiffening. Through rigor mortis heat 

 is developed; some after-death temperatures are remarkably 

 high (see p. 241). 



The rapidity with which rigor mortis sets in differs 

 according to the mode of death. If an animal in perfect 

 health be destroyed, the muscle stiffening is slow to set in 

 and very persistent ; where death is produced by debilitating 

 disease, or in cases where severe muscular exhaustion has 

 preceded death, the rigor mortis may occur so suddenly 

 and pass off so rapidly as occasionally to escape observation, 

 and decomposition also sots in early. The muscles of the 

 tongue appear to me to be the only ones where rigor mortis 

 does not occur, or only incompletely ; the extremity of the 

 tongue in a dead horse is always Qaccid, and hanging out of 

 the side of the mouth. 



After a certain length of time rigor mortis passes oft' and 

 decomposition commences. 



