50 ELEMENTS OF PHYSIOLOGY 



excites impulses in the sensory nerves of the face, which 

 travel to the enlargement at the top of the spinal cord 

 just at the base of the brain, called the spinal bidb, or 

 medulla oblongata (Plate VI). Here it reaches a nerve 

 center which reflects impulses along the nerves that go 

 to the muscle fibers in the walls of the blood vessels, 

 causing them to contract, and the face turns white. Thus 

 we see how closely related are the two master tissues. 



81. If we consider that the nerves reach almost every- 

 where in the body, and that the muscles of the body weigh 

 nearly as much as all other tissues together, we realize how 

 important the master tissues are. Let us count up some of 

 the activities in which the muscles are necessary : swallow- 

 ing, digesting food, breathing, blushing, writing, walking, 

 talking, looking, tasting, chewing, frowning, smiling, laugh- 

 ing, circulation of the blood. There are only a few things, 

 such as hearing, smelling, and feeling, that can sometimes 

 be accomplished without muscles. It is now taught by 

 those who study psychology, or the science of the mind, 

 that emotions of the mind are always simultaneous with a 

 change in the circulation of the blood, and that emotion 

 cannot be felt without a change in the heart or other blood 

 vessels. 



