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ANNUAL REPOET SMITHSONIAN INSTITUTION, 192 8 



4. MEANS OF rRODUCING ODORS FOR RECOGNITION 



Long ago it was stated that most animals emit odors peculiar not 

 only to the individual, variety, race, and species, but also to the genus, 

 family, order, and class, and that these odors are the chief means 

 by Avhich one animal recognizes other animals. Without the aid of 

 the eyes the degenerate human nose is able to distinguish a horse 

 from a cow, a goat from a roe, a dog from a cat, a martin from a 

 fox, a crow from a pigeon, a parrot from a hen, a lizard from a 

 snake, and even a carrion crow from a hooded crow. 



All odors arising 

 from the skin, hair, 

 feathers, or scales of 

 an animal have their 

 sources in secretions or 

 excretions which pass 

 through the skin or 

 integument by special 

 ducts or pores, and not 

 directly by osmosis; 

 in some animals, how- 

 ever, particularly in 

 certain insects, the 

 existence of these 

 pores has not yet been 

 definitely established. 

 T h e scent-producing 

 organs, which may 

 possibly include three 

 types of glands — spe- 

 cial scent glands, 

 sweat glands, and 

 subaceous gland s — 

 have not yet been 

 thoroughly and sys- 

 tematically studied in 

 any order of animals, and in most cases definite and specific functions 

 have not been assigned to the various types. Odors may also be 

 emitted from the body at either end of the alimentary canal, but 

 these probably play no part in recognition among animals. 



Special scent glands have been found in a large number of animals, 

 including numerous insects. They are located in various parts of 

 the anatomy. Some lie in the feet; the secondary function of these 

 is probably to leave scented tracks wherever the animal steps. 



The skin of mammals in particular is characterized by richness 

 in glands, of which there are two kinds; sweat glands (fig. 3, w), 



Figure 3. — Diagram of a section of human skin sliowing 

 epidermis (E) ; dermis (D) ; hair {h), arising from a 

 hair follicle into which empties the secretion of oil or 

 sebaceous glands (s) ; sweat glands {w) and their 

 ducts, which pass in a spiral through the epidermis ; 

 blood vessels (v) ; fat cell (f), and nerve (»), which 

 innervates the sense papilla;. (From Ilcrtwig, after 

 Wiedersheim, slightly modified) 



