CHAPTER III. 



PHYSIOLOGICAL EFFECTS OF LABOUR : FATIGUE. 



141. Conditions of Normal Activity. Any muscular action 

 is accompanied by various physiological effects, which modify 

 the intensity of the respiratory, circulatory and nervous pheno- 

 mena. 



These modifications often attain a degree which is shown by 

 fatigue, this being the normal case. The extreme degree is 

 exhaustion, a pathological state. 



With lesser degrees of fatigue the organism recovers its equili- 

 brium and is completely repaired by rest, notably by the calm and 

 sleep of the night. 



It is therefore important to indicate the physiological effects 

 which are exhibited in a state of activity which is normal, and 

 such that the vital energy is not permanently diminished. 



142. Effects of Work on the Respiration. To study the rhythm 

 and amplitude of the respirations a graphical method is em- 

 ployed. A single or double tyrnpan is secured to the chest by 

 means of a strap. It communicates with another tympan pro- 

 vided with a style, the whole apparatus being called the pneumo- 

 graph (see Technics, 195). A pneumographic trace indicates 

 the following : 



15 to 18 respirations take place per minute when a man breathes 

 in a state of repose. This rhythm varies with age. 



On an average the following results are obtained : 



It will be seen from the pneumographic curve (fig. 139) that 

 the expiration lasts a little longer than the inspiration, and 

 that the two phases succeed each other fairly regularly. 



When working, the rhythm increases and can attain twice its 

 value in repose, i.e., 25 to 35 respirations instead of 18 in an adult, 

 at an external temperature of 12* to 15 C. Also the exercise of 

 effort is marked by prolonged inspirations and short expirations, 

 which is the reverse of the state of affairs in repose. 



