THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL, 



Vol. XII. NOVEMBER, 1891. No. 11. 



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 can Mojithiy Microscopical Journal, Washington, D. C. 



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Introduction to Elementary Biology. 



By henry L. OSBORN, 



HAMLINE, MINN. 



Part VI. — A Specific Life History Considered Biologically. — 



The Frog. 



( Contttiued fron page ^J^.) 



The skin of the frog is not exhausted when we cite its sHme-produc- 

 ingand color functions, for it serves as the medium of the sense of touch 

 and permits the passage of gasses to and from the blood, but at the risk 

 of being incomplete w^here entire completeness would be possible only 

 at the expense of important space it will be best now to look somewhat 

 closely at another set of organs, the ciliated cells of the throat and 

 bronchial passages. 



If the skin of the frog's throat be examined with a power of 50 

 diameters substances on its surface can be seen to move slowly along 

 as if flowing in a gentle current in a definite and constant direction. 

 The same could be seen if the tubes were large enough to inspect 

 readily in the bronchial tubes. In these tubes the current is always up 

 toward the throat and away from the recesses of the lungs. In conse- 

 quence of this constant current particles of dust from the dust-laden air 

 the creature breathes are moved up to and collected in the throat, 

 whence they can be removed when they become annoying. By remov- 

 ing a small piece of this skin to a glass slide in salt solution and teasing 

 it well, then covering it with a glass cover, it can be examined with a 

 power of 300 or 400 diameters. For comparison with these teased 

 specimens one should examine vertical sections of the skin which have 

 been made by histological methods ; by means of the two studies the 

 facts now described can be verified. The skin of the frog's throat is 

 composed of a pavement of minute blocks which we may compare with 

 bricks set upon their ends. These blocks are the cells of the skin mem- 

 brane. They are only one row deep. Each cell is taller than broad 

 and five or six-sided in cross section. The cell presents one end to- 



Copyright, 1891, by C. W. Smiley. 



