90 THE CONTRACTILE TISSUES. 



tial energy of carbon compounds, and not of nitrogen compounds at all. 

 But to this point we shall have to return. 



64. We may sum up the chemistry of muscle somewhat as follows : 



During life the muscular substance is continually taking up from the 

 blood, that is, from the lymph, proteid, fatty and carbohydrate material, 

 saline matters and oxygen ; these it builds up into itself, how we do not 

 know, and so forms the peculiar complex living muscular substance. The 

 exact nature of this living substance is unknown to us. What we do know 

 is that it is largely composed of proteid material, and that such bodies as 

 myosinogen, myoglobulin, and albumin have something to do with the build- 

 ing of it up. 



During rest this muscular substance, while taking in and building itself 

 up out of or by means of the above-mentioned materials is continually giving 

 off carbonic acid and continually forming nitrogenous waste such as kreatin. 

 It also probably gives off some amount of sarcolactic acid, and possibly 

 other non-nitrogenous waste matters. 



During a contraction there is a great increase in the quantity of 

 carbonic acid given off, of lactic acid and some other substance formed 

 giving an acid reaction, a greater consumption of oxygen, though the 

 increase is not equal to the increase of carbonic acid, but as far as we 

 can learn, no increase of nitrogenous waste. 



During rigor mortis there is a similar increased production of carbonic 

 acid and of some other acid-producing substance, accompanied by remark- 

 able conversion of myosinogen into myosin, by which the rigidity of the 

 dead fibre is brought about. 



Thermal Changes. 



65. The chemical changes during a contraction set free a quantity of 

 energy, but only a portion of this energy appears in the " work done," a con- 

 siderable portion takes on the form of heat. Though we shall have hereafter 

 to treat this subject more fully, the leading facts may be given here. 



Whenever a muscle contracts its temperature rises, indicating that heat 

 is given out. When a mercury thermometer is plunged into a mass of mus- 

 cles, such as those of the thigh of the dog, a rise of the mercury is observed 

 upon the muscles being thrown into a prolonged contraction. More exact 

 results, however, are obtained by means of a thermopile, by the help of 

 which the rise of temperature caused by a few repeated single contractions, 

 or indeed by a single contraction, may be observed, and the amount of heat 

 given out approximately measured. 



The thermopile may consist either of a single junction in the form of a needle 

 plunged into the substance of the muscle, or of several junctions, either in the 

 shape of a flat surface carefully opposed to the surface of muscle (the pile being 

 balanced so as to move with the contracting muscle, and thus to keep the contact 

 exact), or in the shape of a thin wedge, the edge of which comprising the actual 

 junctions, is thrust into a mass of muscles and held in position by them. In all 

 cases the fellow-junction or junctions must be kept at a constant temperature. 



Another delicate method of determining' the changes of temperature of a tissue 

 is based upon the measurement of alterations in electric resistance which a fine 

 wire, in contact with or plunged into the tissue, undergoes as the temperature of 

 the tissue changes. 



It has been calculated that the heat given out by the muscles of the 



thigh of a frog in a single contraction amounts to 3.1 micro-units of heat 1 



for each gramme of muscle, the result being obtained by dividing by five 



the total amount of heat given out in five successive single contractions. It 



1 The micro-unit being a milligramme of water raised one degree Centigrade. 



