546 PHYSIOLOGY. 



Cold, which retards chemical phenomena., retards the appear- 

 ance of cadaveric rigidity and prolongs it enormously. 



Influence of Fatigue. The influence of prolonged labor of the 

 muscle upon the premature appearance of rigidity is an indisputable 

 fact. 



Muscular Labor and Urea Excretion. With the ordinary diet of 

 fats, carbohydrates., and proteids, muscular labor greatly increases 

 the output of carbon by the lungs in the shape of carbon dioxide, 

 whilst the nitrogen excreted as urea is slightly, if at all, increased. 

 In a fasting animal work increases the excretion of both the carbon 

 and the nitrogen. The output of carbon is proportional to the work 

 done, the nitrogen not being so closely proportional. Here the mus- 

 cle procures its energy from the proteids, whilst the animal with an 

 ordinary diet uses up mainly the carbohydrates and fats. 



Hence, in muscular exertion the chief foods proteids, fats, and 

 carbohydrates are metabolized in order to set free heat and work. 

 In doing this the muscle prefers to break up the fats and carbo- 

 hydrates rather than the proteids. Hence when muscle fulfills its 

 two chief functions, to produce work and heat, it uses up the fats 

 and carbohydrates and proteids, but the proteids are chiefly used to 

 build up and repair the muscle-substance itself. 



SARCOLACTIC ACID. The production of sarcolactic acid is the 

 more abundant as the muscle has been longer and more strongly 

 excited. 



Myograph. The du Bois-Eeymond induction coil is the one 

 most commonly employed in physiological experiments. When it is 



the swing of the pendulum, is also omitted. Before commencing an experiment 

 the pendulum is raised up (in the figure to the right) and is kept in that position 

 by the tooth (a) catching on the spring-catch (&). On depressing the catch (ft) 

 the glass plate is set free, swings into the new position indicated by the dotted 

 lines, and is held in that position by the tooth (a') catching on the catch (6'). 

 In the course of its swing the tooth (a'), coming into contact with the projecting 

 steel rod (c), knocks it on one side into the position indicated by the dotted line 

 (c'). The rod (c) is in electrical continuity with the wire (a?) of the primary coil 

 of an induction-machine. The screw (d) is similarly in electrical continuity with 

 the wire (y) of the same primary coil. The screw (d) and the rod (c) are armed 

 with platinum at the points at which they are in contact, and both are insulated 

 by means of the ebonite block (e). As long as c and d are in contact the circuit 

 of the primary coil to which x and y belong is closed. When in its swing the 

 tooth (a') knocks c away from d, at that instant the circuit is broken, and a 

 "breaking" shock is sent through the electrodes connected with the secondary 

 coil of the machine and so through the nerve. The lever (I), the end only of 

 which is shown in the figure, is brought to bear on the glass plate, and when at 

 rest describes a straight line, or more exactly an arc of a circle of large radius. 

 The tuning-fork (f), the ends only of the two limbs of which are shown In the 

 figure placed immediately below the lever, serves to mark the time. 



