14 ELEMENTS OF PHYSIOLOGY 



independently of the amount of blood circulating around 

 them, although usually the amount of secretion is greatly 

 influenced by the amount of blood in the skin (Fig. 2). 

 Sometimes the skin is hot from the abundance of blood 

 flowing through it, as during a fever, but it is dry as well 

 as hot because the sweat glands are not acting. A dog 

 does not perspire except through the soles of its feet and 

 through its tongue. Once a curious experiment was tried 

 upon a dog in which the nerves supplying one foot had 

 been severed. This dog was placed in a very hot chamber. 

 Three of its feet perspired profusely ; but the foot which 

 lacked nerves to control its sweat glands was perfectly 

 dry. This shows that nervous control as well as heat 

 is necessary to make the gland cells perform their func- 

 tions. Sometimes, under the influence of excitement or 

 fear, a person breaks out in a profuse perspiration, which 

 is, however, cold, for there is little blood in the skin. 



18. Stimulants and Narcotics. A stimulant is a sub- 

 stance that is usually an enemy to the welfare of the body; 

 it irritates and excites when first taken. This is because 

 of the effort of the system to expel it. After such effort, 

 the body is weaker and more sluggish than before. This 

 effect is called the reaction. There is no known stimulant 

 that does not cause a reaction. A narcotic is a substance 

 that deadens the nerves; this effect does not come as a 

 reaction, but begins as soon as the narcotic is taken. 

 Strychnine is a stimulant ; tobacco is a narcotic. How 

 alcohol is apparently a stimulant but really a narcotic will 

 be explained in another chapter. The toper is said to 

 have a " rum blossom " on his nose. This swollen condi- 

 tion of the blood vessels of the nose is caused by the para- 

 lyzing action of alcohol upon the walls of the blood vessels. 

 The stagnant circulation allows the blood to become purple 

 with impurities. Coffee-drinking often causes the com- 

 plexion to be "muddy." Have you ever noticed any differ- 



