560 MUSCLES. 



in part makes use of a similar artifice in order to regulate the concentra- 

 tion of the nutritive bodies within the protoplasm. 



Rigor Mortis of the Muscles. If the influence of the circulating 

 oxygenated blood is removed from the muscles, as after the death of the 

 animal or by ligature of the aorta or the muscle-arteries (STENSON'S 

 test), rigor mortis sooner or later takes place. The ordinary rigor appear- 

 ing under these circumstances is called the spontaneous or the fermentative 

 rigor, because it seems to depend in part on the action of an enzyme. 

 A muscle may also become stiff for other reasons. The muscles may become 

 momentarily stiff by warming, in the case of frogs to 40, in mammalia 

 to 48-50, and in birds to 53 C. The heat-rigor depends upon the coagula- 

 tion of certain proteins, and its occurrence at lower temperatures in 

 cold-blooded as compared with warm-blooded animals is due, accord- 

 ing to v. Ft)RTH,,to the fact that in the first a soluble myogen fibrin occurs 

 preformed in the muscle which coagulates at 30-40 C., while in the 

 warm-blooded animals .the coagulating substance is musculin (myosin 

 of v. FURTH) which coagulates at a higher temperature. According 

 to INAGAKI l the various stages in contractions occurring on heating a 

 muscle (frog) do not correspond to those of the coagulation of the pro- 

 tein which would occur on heating the muscle plasma, and this probably 

 depends upon the fact that the reaction of the muscle changes on heating 

 with the formation of lactic acid. Distilled water may also produce 

 a rigor in the muscles (water-rigor). Acids, even very weak ones, such as 

 carbon dioxide, may quickly produce a rigor (acid-rigor), or hasten its 

 appearance. A number of chemically different substances, such as 

 chloroform, ether, alcohol, ethereal oils, caffeine, and many alkaloids, 

 produce a similar effect. The rigor which is produced by means of acids 

 or other agents which, like alcohol, coagulate proteins must be considered 

 as produced by entirely different processes from those causing spontaneous 

 rigor. 



When the muscle passes into rigor mortis it becomes shorter and 

 thicker, harder and non-transparent, and less ductile. The acid part 

 of the amphoteric reaction becomes stronger, which is explained by most 

 investigators by the assumption of a formation of lactic acid. There is 

 hardly any doubt that this increase in acidity may at least in part be due 

 to a transformation of a part of the diphosphate into monophosphate 

 by the lactic acid. The reports in regard to the presence or absence 

 of free lactic acid in the rigor-mortis muscle are contradictory. 2 Besides 



1 Zeitschr. f. Biol., 48. See also E. B. Meigs, Amer. Journ. of Physiol., 24. 



2 It is impossible to enter into the details of the disputed theories as to 

 the reaction of the muscles, etc. We shall only refer to the works of Rohmann, 

 Pfliiger's Arch!, 50 and 55, and Heffter, Arch. f. exp. Path. u. Pharm., 31 and 38 



