554 MUSCULAR RIGIDITY. 



ing blood containing oxygen through excised muscles, C. Ludwig and Al. Schmidt 

 found that the onset of rigidity was retarded for a long time; this did not occur, 

 however, with blood deprived of oxygen. After considerable loss of blood, rigidity 

 sets in relatively early. If an artificial circulation be kept up in the dead muscles 

 of a frog by means of feebly alkaline fluids, rigidity does not occur. 



Previous section or paralysis of the motor nerves results in delayed onset of 

 rigidity in the relaxed muscles. The reason is found in the greater abundance of 

 blood in these muscles, in consequence of associated paralysis of the vasomotors, 

 the alkaline blood remaining in the muscles even after death, while the arteries 

 in other parts of the body become empty. This view is supported by the fact 

 that rigidity appears much later in fish whose medulla oblongata is suddenly 

 destroyed than in those that die slowly. According to Ewald and Willgerodt the 

 labyrinths of the ear, as organs controlling tone, likewise have an influence on the 

 course of rigidity. 



Freezing and thawing cause rigidity to set in more rapidly, and it is 

 favored likewise by mechanical injury. 



Continuous passive movements may retard the onset of rigidity, but on their 

 cessation their rigidity sets in all the more rapidly. Rigidity that has already 

 developed may be overcome by forced movements, but it may set in again. 



Rigidity may be induced artificially: 



1 . By heat (heat-rigor) , which causes coagulation of the myosin in cold-blooded 

 animals at 40, in mammals at from 45 to 47 C., and in birds at about 53 C. 

 Under such circumstances there is marked excretion of carbon dioxid, but less 

 after previous tetanization. Protoplasm, for example of the amoeba, is similarly 

 subject to heat-rigor. 



The degree of heat required to bring about rigidity is the higher the longer 

 the muscles have been excised. If the muscles of a frog in a state of cadaveric 

 rigidity be heated, the remaining proteids undergo coagulation successively, and 

 the muscle becomes still more rigid as a result of these coagulative processes. 



2. Saturation with water induces water-rigor, with the development of an 

 acid reaction, in consequence of the coagulation of the globulin-substances, the 

 excretion of carbon dioxid not being increased. 



If the thigh of a frog be ligated, and the muscles, deprived of their skin, be 

 immersed in warm water, they will become rigid. On loosening the ligature a 

 slight degree of rigidity may disappear through restoration of the circulation. On 

 the other hand, a more marked degree of rigidity can be removed only by placing 

 the leg in a 10 per cent, solution of sodium chlorid, which will dissolve the myosin- 

 coagulum. 



3. Acids, even weak acids such as carbon dioxid, induce rapid acid-rigor. 

 This is probably different from normal rigidity, as the muscle does not develop 

 free carbon dioxid. Injection of from o.i to 0.2 per cent, solutions of lactic or 

 hydrochloric acid into the vessels of frogs' muscles causes immediate rigidity, 

 which can be overcome by 0.5 per cent, acid, and also by a neutralizing solution 

 of sodium bicarbonate, or 13 per cent, solution of ammonium chlorid. The acids 

 enter into combination with the myosin. 



4. Among poisons and other substances, the following promote rigidity: 

 Caffein, quinin, digitalin, veratrin, hydrocyanic acid, also oils of mustard, fennel, 

 and anise, and, when placed in direct contact with the muscles, potassium sulpho- 

 cyanid, ammonia, metallic salts, alcohol, ether, chloroform. Chloroform, acetic 

 acid, and heat induce rigidity with shortening; ammonia, on the other hand, 

 rigidity without shortening. 



The position of the entire body during rigidity is usually that which it occupied 

 at death. The position of the limbs corresponds to the resultant of the various 

 degrees of muscle-tension. If the limbs occupied another position before death, 

 they are frequently seen to move during the onset of rigidity. The arms and 

 fingers especially are readily flexed. If the rigidity develops with especial firmness 

 and rapidity in certain groups of muscles, an unusual position may be assumed, 

 for example the fencing attitude of cholera-cadavers. If the rigidity occurs rap- 

 idly, the body at times remains in the same position that it occupied at the moment 

 of death, for example on the battle-field. Under such circumstances, however, 

 the contracted muscle never passes immediately into a condition of rigidity, a 

 period of relaxation intervening, even though short. 



Muscles scalded by immersion in boiling water do not become rigid; neither 

 do they become acid, nor evolve free carbon dioxid. Muscles coagulated by 

 concentrated alcohol or by immersion in concentrated solutions of sodium chlorid , 

 potassium nitrate, sodium and magnesium sulphate, do not yield an acid reaction. 



