128 PHYSIOLOGY AND HEALTH. 



uted throughout the whole respiratory organs. The blood- 

 vessels ( 225, p. 103) proceed from the heart in large trunks, 

 and, like the air-tubes, are divided and multiplied until they 

 terminate in minute branches of imperceptible size, which 

 lie in contact with, and spread over, the air-cells. Then 

 these little blood-vessels are again gathered together into 

 larger and larger tubes, until, at last, they form two large 

 trunks, that enter the heart. These trunks are of the same 

 size as those which left the heart to carry the blood to the 

 lungs. 



280. The windpipe, or trachea, is composed of somewhat 

 stiff rings of cartilage or gristle, so that it is easily felt in 

 the front of the throat. The upper end of this tube is usu- 

 ally open; but the epiglottis ( 20, 21, 22, p. 16) is 

 placed there to cover over and protect this passage when- 

 ever the food passes over it, on its way from the tongue to 

 the oesophagus. But, when we are not swallowing, this 

 valve stands open. 



281. The upper end of the windpipe opens into the back 

 chamber of the mouth, by- a narrow chink, called the glottis 

 This is made by the approximation of the two sides of the 

 tube, so that the air may produce sounds when it passes be- 

 tween them. Some muscles, which are attached to these 

 sides, draw them more closely together, or allow them to 

 separate. By thus opening or narrowing this chink, the 

 sounds which are made by the air passing through it, are va- 

 ried. -This is the organ of voice ; and these sounds are the 

 various tones which we utter in language, in singing, or in 

 crying. When this part of the windpipe is diseased by 

 what is called, a cold in the throat or otherwise, these tones 

 are changed, and often destroyed. A man then loses the 

 control of his voice, and can neither sing nor talk as he does 

 in health. Sometimes the voice is entirely destroyed or sus- 

 pended, and then the sufferer can only speak with the mouth 

 in a whisper. A gentleman, whom I have seen while writing 

 this chapter, has not been able to speak a loud word for three 

 months, in consequence of ulceration about the glottis. 



