GREGG] THE SKIN 301 



magnifying glass, such as every teacher or schoolroom may well 

 have and such as is used in botany work in the analysis of 

 flowers, etc. Look at the back of the hand first and notice how 

 rough and seemingly scaly the skin of the hand is. Recall how 

 on warm days or when one is sweaty one can readily scrape stuff 

 from the surface of seemingly clean skin. If one were to let 

 some of this stuff (called scurf) dry up and then examine it 

 with a simple microscope, it would be found to be made up of 

 a lot of scales, skin cells dried together. These outside cells 

 of the body are dead and non-sensitive, as any schoolboy knows, 

 who, in the absence of more interesting work, spends part of his 

 time in sticking pins under this dead outer layer of the skin, 

 (b) Once more look through the magnifier at the skin of the 

 hand, this time on the palm. Notice the little ridges. Now look 

 very sharply for tiny little depressions along the top of the 

 ridges. The depressions are as if they had been made by gentle 

 pin pricks, and average a little less distance apart than the width 

 of the ridges. If one is sweating just a very little, extremely 

 tiny drops of water may be seen at each of the depressions. This 

 is because here are the outlets of the sweat pores of the skin. 

 Similar depressions can be found all over the skin, but they are 

 not so readily made out elsewhere. 



2. Demonstration of "insensible" perspiration. — We know 

 that moisture stands out over the skin when we are quite warm 

 and the previous study as well as our general knowledge tells 

 us that the moisture comes out of the skin itself. On colder days 

 we are not so certain about the presence of this moisture. To 

 find out about it we need a day or a place where the tempera- 

 ture is, say between .50^ and 60° F. In such a temperature a 

 pupil may put his hand into a quart fruit-jar, not allowing the 

 bare skin to touch the jar, and stopping up the unoccupied part 

 of the mouth of the jar with a handkerchief. Thrusting a ther- 

 mometer tube (a dairy thermometer is excellent) into the jar 

 the temperature will be found to be between 60° and 70° F. 

 To provide a "control" for the experiment so as to make sure 

 of the conclusions, have at hand an empty and lidless jar in 

 the place where the experiment is going on. After ten minutes 

 examine the inner surface of each jar. On the one the hand is in 

 there appears a film of moisture, but not in the other. So it 

 appears that a little perspiration is going on even when the 

 surrounding temperature is as low as 50° or 60° F. 



3. Are there decay germs on the surface of the skin? — (a) 

 We are told that decay is caused by germs and we learned from 



