224 PHYSIOLOGY FOR DENTAL STUDENTS. 



when evaporation is slow, because of saturation of the air, ;m<l 

 heat is no longer given off quickly by the body, the individuals 

 in the room become very uncomfortable. An electric fan, which 

 distributes the air evenly over the room and thus quickens the 

 removal of the warm moist air immediately surrounding the 

 body, adds much to the comfort of the person. While it. is not wise 

 to discourage fresh air in public offices and private houses, it is 

 absolutely necessary that the ventilating engineer should pay 

 heed to something besides the percentage of oxygen and carbon 

 dioxide in the room. He should also direct his efforts towards 

 cooling and increasing the circulation of the air that surrounds 

 the bodies of the individuals, by setting the air in motion by 

 means of fans. 



The conditions of temperature, the moisture, and the windless 

 atmosphere found in public rooms and homes diminish the heat 

 loss of the body and thus the heat production, which means that 

 the activity of the occupants must be less. A reasonable tem- 

 perature with a relatively low percentage of moisture, and ordi- 

 nary care in providing fresh air, will maintain the proper hy- 

 gienic conditions of a room. 



The Voice. 



The voice-producing mechanism in man consists of the trachea, 

 through which the air is blown from the lungs; the larynx, the 

 modified upper portion of the trachea, which contains the vocal 

 cords; and the pharynx, and upper air passages. The larynx 

 forms the entrance into the trachea. It is composed of a number 

 of cartilaginous plates which are united in a manner to form a 

 box. Stretched from front to back on each side across the upper 

 portion of the larynx are thin sharp-edged membranes, the voctil 

 cords. The attachments of the muscles to the cartilages and the 

 articulations of the several cartilages with each other, are so ar- 

 ranged as either to tighten or loosen the tension, or increase or 

 decrease the opening between the edges of the cords. The cleft 

 between the cords is called the glottis. The length of the vocal 

 cords varies from 11 to 15 mm., being longer in men than in 

 women and children. Branches of the vagus and the spinal ac- 



