CHAP, ii.] THE CONTRACTILE TISSUES. 101 



Further, the change from the living irritable condition to that of 

 rigor mortis is accompanied by a large and sudden development of 

 carbonic acid. 



It is found moreover that there is a certain amount of parallel- 

 ism between the intensity of the rigor mortis, the degree of acid 

 reaction and the quantity of carbonic acid given out. If we 

 suppose, as we fairly may do, that the intensity of the rigidity is 

 dependent on the quantity of myosin deposited in the fibres, and 

 the acid reaction to the development if not of lactic acid, at least 

 of some other substance, the parallelism between the three products, 

 myosin, acid-producing substance, and carbonic acid, would suggest 

 the idea that all three are the results of the splitting-up of the 

 same highly complex substance. No one has at present however 

 succeeded in isolating or in otherwise definitely proving the exist- 

 ence of such a body, and though the idea seems tempting, it may 

 in the end prove totally erroneous. 



62. As to the other proteids of muscle, such as the albumin 

 and the globulin, we know as yet nothing concerning the parts 

 which they play and the changes which they undergo in the living 

 muscle or in rigor mortis. 



Besides the fat which is found, and that not unfrequently in 

 abundance, in the connective tissue between the fibres, there is 

 also present in the muscular substance within the sarcolemma, 

 always some, and at times a great deal, of fat, chiefly ordinary fat, 

 viz. stearin, palmitin, and olein in variable proportion, but also 

 the more complex fat lecithin. As to the function of these several 

 fats in the life of the muscle we know little or nothing. 



Carbohydrates, the third of the three great classes in which we 

 may group the energy holding substances of which the animal 

 body and its food are alike composed, viz. proteids, fat and carbo- 

 hydrates, are represented in muscle by a peculiar body, glycogen, 

 which we shall have to study in detail later on. We must here 

 merely say that glycogen is a body closely allied to starch, having 

 a formula, which may be included under the general formula for 

 starches x (C 6 H 10 5 ), and may like it be converted by the action of 

 acids, or by the action of particular ferments known as amylolytic 

 ferments, into some form of sugar, dextrose (C 6 H 12 O 6 ) or some 

 allied sugar. Many, if not all, living muscles contain a certain 

 amount, and some, under certain circumstances, a considerable 

 amount of glycogen. During or after rigor mortis this glycogen is 

 very apt to be converted into dextrose, or an allied sugar. The 

 muscles of the embryo at an early stage contain a relatively 

 enormous quantity of glycogen, a fact which suggests that the 

 glycogen of muscle is carbohydrate food of the muscle about to be 

 wrought up into the living muscular substance. 



The bodies which we have called extractives are numerous and 

 varied. They are especially interesting since it seems probable 

 that they are waste products of the metabolism of the muscular 



