AND PHYSIOLOGY. 



299 



the skin with the finest needle, when a drop of blood is sure 

 to follow. The nerves of sensation too are very abundant, as 

 we know by the insertion of a pin into any part of the body, 

 which invariably pains us, because we have wounded a nerve, 

 and not an expanded surface, like a membrane. 



524. Sebaceous or Oil Glands. — The Sebaceous Glands 

 are small elongated sacs which are generally gathered in 

 clusters about each of the 



hairs of the body, varying Fig. 290. 



in number from four to twen- 

 ty. They pour their secre- 

 tion into the hair-canals near 

 their orifices, and are most 

 abundant in the parts of the 

 body most exposed, as in the 

 skin of the nose. Their se- 

 cretion in most places resem- 

 bles fat, although in the pas- 

 sage of the external ear a 

 substance resembling wax 

 (cerumen) is poured out. 



524a. Parasite in the 

 Sebaceous Glands. — It is a 

 fact curious, if not at first 

 sight revolting, that there is 

 very constantly found in the 

 outlets to many of the sebaceous glands a parasitic animal, as 

 represented by the cut. (Fig. 291, p. 300.) The occurrence 

 of this animal in almost every individual has led one anat- 

 omist to call it a " denizen" of the human body. 



525. Sweat Glands. — Length of Sweat Tube in the 

 Human Body. — The Sudoriparous or Sweat Glands essen- 



A View of the Cerumen Gland 

 formed by the Contorted Tubes. 1, 1; 

 The Tubes. 2, The Excretory Duct. 

 3, The Vessels supplying it. 



What of the nerves in the corium ? 524. What are the sebaceous glands ? Where are 

 they the most abundant ? What is their secretion ? 524 a. What is said of the parasite 

 in the skin? 



