56 



breathe again is experienced ; then allow respirations to recur 

 and record one or two. Measure the length of the absence 

 of breathing (Apncea). 



Now breathe deeply and forcibly for about two minutes, so 

 as to clear the C0. 2 out of the blood, recording the last two or 

 three respirations. Then hold the breath as above, and 

 measure the length of the absence of breathing, and compare 

 it with the last. Another student should observe any change 

 in the appearance of the face, and must examine the pulse. 



7. Effect of mental and muscular work on the circulation and 

 respiration. 



A. 1. Have ready the apparatus to record the respiration 

 from the nostril of a fellow student. 



2. Place the bag of the Riva Rocci apparatus round his arm. 



3. The subject holds the other hand out from the side, and 

 the observer determines at what level of the hand the veins 

 disappear while the subject is sitting still. 



4. Note the colour of the face. 



B. Having recorded the respiration and systolic, blood 

 pressure, counted the pulse and measured the height of the 

 hand above the heart at which the veins collapse, make 

 the subject perform 10 minutes' strenuous mental work and 

 again examine and record systolic arterial blood pressure, 

 pulse, venous pressure and respiration, and note the colour of 

 the face. 



C. Now make him take strenuous muscular exercise till he 

 is breathless, and repeat all the observations. 



Formulate your conclusions as regards the effect of mental 

 work and of muscular work upon 

 The rate of the heart. 

 The systolic arterial pressure. 

 The venous pressure. 

 The rate and depth of respiration. 



8. Demonstration of the influence of CO,, and of various nerves 

 on the breathing of an anaesthetised rabbit. 



