94 EXPERIMENTAL PHYSIOLOGY 



out the parts which act in removing the waste. (The artery 

 brings in the blood, which gives up its waste in the glomer- 

 ulus. This waste is collected by the tubule and emptied by 

 it into the ureter. The capillaries collect the blood which 

 has been cleared of its waste, and return it to the vein.) 



NOTE. Prepared sections of injected and stained cortex may be 

 shown and the following parts demonstrated: Malpighian bodies, 

 uriniferous tubules, and capillaries. 



LXII. STUDY OF THE SKIN. 



Apparatus. Prepared slide of epidermis (that from the sole of 

 the foot preferred, from its thickness), a vertical section of a hair, 

 compound microscope, needle, scissors. 



Directions. A. Surface Study of the Skin Layers. Ster- 

 ilize a needle by holding it in a flame a moment. Run it 

 carefully under the thin outer layer of skin at the base of 

 the thumb. (This layer is called the cuticle or epidermis.) 

 Does the wound cause any pain? Are there any nerves in 

 this layer? Does the wound bleed? Does the epidermis 

 contain any blood vessels? With the needle tear off a little 

 of this epidermis. What is its color? consistency? Where 

 is it thickest on the hand? Why? Where else on the body 

 do you find similar thickening? 



What is the color of the skin layer (dermis) 'under this 

 epidermis? Prick it with the needle. Is it sensitive? 

 Does it contain blood vessels? Examine its surface and note 

 that it is ridged. A magnifier will show that these ridges 

 are made up of a series of points, or papillce. (Each papilla 

 marks the end of a nerve of touch. These nerve endings 

 are called on that account tactile organs; see Fig. 45.) 



