MUSCLE 587 



contraction : the rigor passes off as the contraction passes off, although 

 the ' resolution ' of a rigid muscle takes days, the relaxation of an 

 active muscle a fraction of a second. The disappearance of rigor 

 is not dependent on putrefaction ; it takes place when growth of 

 bacteria is prevented (Hermann). 



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 begin to die, a myosin ferment, which 

 aids coagulation^ is developed in dead or dying muscle. But it is easy 

 to make too much of the apparent analogy between the clotting of 

 muscle and the clotting of blood, and 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. 



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 normal 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 aortse can with- 

 stand even a temperature of 48 for a short time. An excised mam- 

 malian 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 sarcolactic 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 ^ C. 

 This is probably due chiefly to the increased chemical change, and 

 only to a slight extent to the physical alteration in the myosin. 



When muscle is at once raised to a temperature of 75 to 100 C, 

 and all the proteids thus coagulated by heat, there is also an increase 

 in the discharge of carbon dioxide (Fletcher), and the reaction be- 

 comes distinctly acid to blue litmus, although still alkaline to red. 

 This is the easiest way of obtaining a maximum. evolution of carbon 

 dioxide from an excised muscle. It is highly improbable that a 

 marked production of carbon dioxide should take place in heat- 

 coagulated proteids. We must therefore suppose that the character- 

 istic decomposition associated with rigor mortis can complete itself 

 in the brief space that elapses between the application of the heat 

 and the heat-coagulation of the proteids. This decomposition is 

 wanting in the so-called rigor caused by water, which is not a true rigor, 

 and causes no increase in the carbon dioxide given off. Chloroform, 

 on the other hand, produces a marked increase in the carbon dioxide 



