NUTRITION . 89 



then of the arms, gradually passing downward until the whole 

 body is stiff. This begins usually soon after death, but may be 

 delayed for several hours, and lasts until putrefactive changes have 

 set in, when the body relaxes. All muscles are affected, plain as 

 well as striped. 



What is the cause of rigor mortis ? 



Coagulation of the muscle-plasma. 



What is the post-mortem rise of temperature ? 



After death there is considerable rise of the temperature of the 

 body, which is very marked during the progress of rigor mortis. It 

 may amount to 5 or 10 F., or even more. 



What changes occur in muscle after death ? 



The muscles become set in contraction, and their reaction becomes 

 acid from the development of lactic acid. 



How do the voluntary muscles act? 



They act as the power which moves the bones in their function 

 as levers. Each of the three classes of levers is illustrated in the 

 body : (1) Fulcrum between power and weight : ham-string mus- 

 cles acting upon the ischium to raise the body from a stooping 

 position ; hip joint, fulcrum. (2) Weight between power and ful- 

 crum : depressors of lower jaw acting against the tension of the 

 temporals, etc., with temporo-maxillary articulation for fulcrum. 

 (3) Power between weight and fulcrum : biceps of the arm in 

 raising the forearm, with elbow-joint as fulcrum. 



How do the involuntary muscles act? 



They do not have attachments to the hard parts, but enter into 

 the composition of the walls of hollow organs which require elas- 

 ticity and variation in size. The heart and arteries, as well the 

 digestive tract, furnish numberless examples of their action. They 

 are often rhythmical in their action (peristalsis), and the stimula- 

 tion of this class of muscles does not cause a tetanus (except the 

 heart), but a succession of alternate contractions and relaxations. 



NUTRITION. 

 What is nutrition ? 



By nutrition we mean the physiological principles which preserve 

 the normal conditions of the structure and function of the body, SG 



