THE LARYNGOSCOPE. 251 



3. Study the construction and mode of using a gas-pump for 

 the analysis of blood-gases. 



4. The laryngoscope is used to investigate the condition of the 

 pharynx, larynx, and trachea. Various forms are in use, but they 

 all consist of (1) One or more small usually circular plane 

 mirrors fixed to a metallic rod at an angle of 120, the metallic 

 rod fits into a suitable handle, and is fixed by means of a screw. 



Fig. 116. Hey wood's Experiment. 



(2) A large concave mirror of about 20 cm. focus perforated 

 with a hole in the centre, and secured to the operator's forehead 

 by means of a circular band passing round the head. The 

 mirror itself is fixed in a ball and socket joint so that it can 

 be moved freely in every direction. 



A. Practise first of all on a model of the head and larynx pro- 

 vided for the purpose. 



B. On a Living Person. (a.) Place the patient upright in 

 a chair. A good source of artificial light e.g., a suitable 

 Argandlamp is placed near the side of the patient's head, a 

 little above the level of his mouth. The new incan- 

 descent lamp gives a brilliant, clear, and steady light. 

 M. Mackenzie's rack-movement lamp is a most convenient 



