116 EXPERIMENTAL PHYSIOLOGY 



results of the analysis along with a diagrammatic curve of the 

 breathing. It will be found that the CO 2 tension is greatly 

 lowered by the forced breathing (what is the reason?) and that 

 normal breathing returns at a tension which is decidedly below 

 the normal. How do you explain this result? 



Repeat this experiment with the difference that the last of the 

 deep inspirations is taken from a rubber bag containing oxygen. 

 Note the duration of the apnoea, the occurrence of cyanosis 

 and the alveolar CO2 tension at the return of breathing. Ex- 

 plain the cause for any changes from the previous results. 



When the forced breathing is kept up for some time, marked 

 changes occur in the acid base equilibrium of the blood because 

 of the blowing off of CO 2 . A condition of alkalosis results and 

 the kidneys respond by excreting urine with relatively less 

 acid than normal. The alkalosis also causes various symptoms 

 the most striking of which affect the nervous system. 

 Experiment 49f . Measure the alveolar CO 2 and the total acidity 

 of the urine of a person who has not recently performed the 

 forced breathing experiment. For the latter purpose, shake 

 about 15 c.c. of urine with about 0.5 gm. of a soluble oxalate, 

 filter, and titrate 10 c.c. of the nitrate against 0.05 N NaOH 

 using phenolphthalein as indicator. Also test the knee jerks 

 (p. 105). Have this person breathe deeply for half an hour, 

 unless the process causes great discomfort when it should be 

 terminated earlier. At frequent intervals observe the pulse, 

 test the knee jerks, look for evidence of venous congestion 

 (cyanosis) and test the excitability of the seventh nerve by 

 tapping with the finger at the point of its emergence from the 

 skull. In a normal person this does not cause any twitching 

 of the face muscles but as alkalosis developes such occurs and 

 becomes progressively more marked. (Chvosek's sign for 

 tetany). Also examine carefully for the appearance of tonic 

 contractions of the flexor and adductor muscles of the hand and 

 forearm. Towards the end of the period of forced breathing 

 this other symptom of tetany will often be quite evident but 

 if not so it can be made to develop by constricting the arm by 

 means of a blood pressure cuff, or a rubber band. (Trousseau's 

 sign for tetany). After discontinuance of the forced breathing 



