STUDY OF EXCRETION. 83 



needle point a little distance into the 

 tissue lying beneath the epidermis. 



a. Is the tinder skin (dermis) supplied 



with blood-vessels? How do you 

 know? 



b. Is the dermis supplied with nerves? 



How do you know? 

 E. Blood system in the skin. 



1. Press the finger of the right hand on the 



back of the left hand; quickly remove 

 the finger. What difference do you note 

 in the color of the spot pressed and in the 

 skin about this spot? Give an explana- 

 tion of this difference. 



2. From the preceding experiment can you ex- 



plain the cause of sudden paleness in the 

 face? 



3. State the difference in the relative quantity 



of blood flowing through the cheek when 

 it is flushed and when it is pale. 



43. STUDY OF EXCRETION. 



A. Excretion from sensible perspiration. 



1. Find the exact weight of your body imme- 



diately after breakfast. Record the fig- 

 ure. 



2. Exercise vigorously for several hours with- 



out eating or drinking. 



3. Find again the weight of the body. Do you 



note any difference in weight? 



