414 NATURE'S TEACHINGS. 



by the contained fire, and expose a very large surface of hot 

 metal to the air. Thus the heat, instead of being wasted by 

 being drawn through the flue or chimney, is thrown into the 

 room, and keeps up a perpetual supply of warm air. 



THAT 1he invention of this stove is an ingenious one nobody 

 can deny. JBut Nature has been long in advance of Art in the 

 way of exposing as large a surface as possible with the least 

 expenditure of space. 



Very familiar examples of this structure may be found in the 

 many creatures which inhabit the waters and breathe by means 

 of gills, which extract the oxygen of the water. 



Take, for example, a Lobster or a Crab, open it, and look at 

 the white, pointed, uneatable objects which are popularly called 

 " ladies' fingers." These are the gills, or breathing apparatus, 

 and their structure is really wonderful. They are composed 

 of innumerable laminae, or very thin plates, covered with an 

 exceedingly fine membrane, and placed closely side by side, 

 but with sufficient distance between them to allow the water 

 to percolate the whole structure. 



With the aid of an ordinary pocket lens the observer may 

 make out a most wonderful system of blood-vessels, which per- 

 meate every one of the myriad laminae, and which extract the 

 life-giving oxygen from the water as it passes between them. 



Then, to pass to animals of a higher order, take the gills 

 of fishes. Any fish will do, provided that it be fresh, and, if 

 it can be examined immediately after death, so much the better. 

 Taking things reciprocally, the gills of the fish and the laminae 

 of the stove, are identical in principle, namely, the exposure of 

 much surface with little loss of space. 



If possible, the observer should inject the blood-vessels of 

 the gills with the conventional crimson and blue wax, showing 

 the currents of the arterial and venous blood. Each lamina 

 forms a most wondrous object, and may be gazed upon for weeks 

 with increasing admiration. 



Every one who has watched the habits of fishes must have 

 noticed that in running waters they always have their heads 

 against the stream, and do not greatly care about shifting their 

 positions. 



In still waters, especially such as those of the ordinary glass 



