674 A MANUAL OF PHYSIOLOGY. 



Why does coagulation of myosin occur at the death of the 

 muscle ? To this question no clear answer can be given. Some 

 have looked on the process as analogous to the clotting of blood 

 when it is shed, and it has even been suggested that just as a 

 fibrin ferment is developed when the leucocytes and blood- 

 plates begin to die, a myosin ferment, which aids coagulation, is 

 developed in dead or dying muscle. But no clear proof has been 

 given of the existence of such a ferment. And it is easy to make 

 too much of the apparent analogy between the clotting of muscle 

 and the clotting of blood, for there are differences as well as 

 resemblances. For instance, the addition of potassium oxalate 

 does not prevent coagulation of muscle extracts, as it does of 

 blood and blood-plasma. The development of lactic acid in the 

 muscle is not the primary cause of the coagulation which con- 

 stitutes the essential feature of rigor mortis, although after rigor 

 has occurred direct precipitation of hitherto unclotted muscle 

 proteins may be induced by the acid, or the acid salts produced 

 in its presence. Deficiency of oxygen is associated with the 

 occurrence of rigor mortis, as it is with the accumulation of lactic 

 acid, and a developing rigor can be abolished by oxygen, and 

 its onset long or indefinitely delayed. When strict asceptic 

 technique is observed an excised sartorius muscle of the frog 

 may remain irritable in sterile Ringer's solution, even without 

 oxygenation, for as long as three weeks (Mines) . 



Various influences affect the onset of rigor. Fatigue hastens 

 it ; heat has a similar effect ; the contact of caffeine, chloroform, 

 and other drugs causes most pronounced and immediate rigor. 

 Blood applied to the cross-section of a muscle first stimulates the 

 fibres with which it is in contact, and then renders them rigid. 

 But it is to be remembered that normally the blood does not 

 come into direct contact even with the sarcolemma, much less 

 with its contents. 



The effect of heat is of special interest. A skeletal muscle of 

 a frog, like the gastrocnemius, if dipped into physiological saline 

 solution at 40 or 41 C. goes into rigor at once ; the frog's heart 

 requires a temperature 3 or 4 higher ; the distended bulbus 

 aortae can withstand even a temperature of 48 for a short time. 

 An excised mammalian muscle passes into immediate rigor at 

 45 to 50. In heat rigor the reaction of the muscle becomes 

 strongly acid owing to the formation of lactic acid, and the 

 production of carbon dioxide is also increased. Heat rigor 

 resembles in these respects a greatly accelerated rigor mortis. 

 A small quantity of heat is produced, and the temperature of 

 the muscle may be raised as much as ^0 C. This is probably 

 due chiefly to the increased chemical change, and only to a slight 

 extent to the physical alteration in the myosin. 



