306 RESPIRATION AND EXCRETION 



Method c. Weigh yourself just before taking exercise in 

 the gymnasium. Weigh yourself at the end of the period. 



Observation. What is the loss in weight ? Why is there 

 a loss, if any ? 



Conclusion. What is another function of the skin ? 



Method d. Wrap the bulb of a thermometer with a strip of 

 cloth, and wet it with water of the same temperature as the 

 room. Let it stand a short time near a thermometer with a 

 dry bulb. 



Observation. Read the two thermometers. Do they agree ? 

 What difference do you note ? Note. As water or any other 

 liquid evaporates, it uses heat, which is taken from near-by 

 substances. 



Conclusion. What caused the wet thermometer to read 

 differently from the dry one ? 



Method e. Place a few drops of ether or alcohol on the 

 back of the hand and note results. 



Observations. 1. What happens to the liquid ? 



2. What is the effect on the hand ? (What sensation ?) 



Conclusions. 1. What do you conclude regarding the effect 

 of evaporation on temperature ? 



2. Where did the moisture come from that collected on the 

 inside of the bell jar ? W T hat is it called ? 



3. What is given off at all times by the skin? 



4. What is its function ? 



Method f. Examine the palm of the hand or the inside of 

 the fingers where they are ridged with a hand lens, and see if 

 you can find very small pits (sweat or perspiration pores) on 

 the ridges. 



Observation. Where are the pores located ? Are there few 

 or many ? 



b. Structure (Optional) 



Method g. Study a prepared slide, showing cross section of the 

 skin. Use low power objective, or study any good Figure. 



Observations. 1. Find two layers of the skin, an outer (epidermis) 

 and an inner (dermis). 



