262 PHYSIOLOGICAL CHEMISTRY. 



phoric acid. Next in amount we have sodium and magnesium, and 

 lastly calcium, chlorine, and iron oxide. Sulphates only exist as 

 traces in the muscles, but are formed by the burning of the proteids 

 of the muscles, and therefore occur in abundant quantities in the 

 ash. The muscles contain such a large quantity of potassium and 

 phosphoric acid that potassium phosphate seems to be unquestion- 

 ably the predominating salt. Chlorine is found in such insignifi- 

 cant quantities that it is perhaps derived from a contamination with 

 blood or lymph. The quantity of magnesium is about double that 

 of calcium. These two bodies, as well as iron, occur only in very 

 small amounts. 



The gases of the muscles consist of large quantities of carbon 

 dioxide, besides traces of nitrogen. 



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

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

 the animal or by tying the aorta or the muscle-arteries (STEP- 

 SON'S test), rigor mortis, sooner or later takes place. The ordinary 

 rigor appearing under these circumstances is called the spontaneous 

 or the fermentive 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. (heat-rigor). Distilled water may also produce a rigor in 

 the muscles (water-rigor). Acids, even when very weak, 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, caff em, and many alka- 

 loids, produce a similar effect. That rigor which is produced by 

 means of acids or other agents which, like alcohol, coagulate 

 albumin must be considered as produced by entirely different pro- 

 cesses than the spontaneous rigor. 



The time within which the spontaneous rigor occurs depends 

 upon the temperature; a low temperature retarding and a high 

 temperature hastening its appearance. Muscular activity also exer- 

 cises an appreciable influence on the rigor of the muscles, for a 

 previous active contraction accelerates the rigor of the muscles; the 

 mechanical abuse. of the muscles acts in the same way. The appear- 

 ance of spontaneous rigor is under the influence of the central nerv- 



