198 THE BIOLOGY OF THE FROG chap. 



inward. Chloroform and other depressants decrease the 

 rate of passage of fluid from without and increase its rate 

 of passage from within. These differences in the rate of 

 the transmission of fluids in different directions tend to dis- 

 appear after the skin dies. 



The amount of fluid that can be forced through the skin 

 under pressure depends also upon the direction of flow. 

 Cima found that as much water under a pressure of i o cm. 

 of mercury would pass through the skin of the frog from 

 within outward in five minutes as would pass through in 

 the reverse direction in thirty-seven minutes. 



Of the excretory function of the skin of the frog practi- 

 cally nothing is known. 



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Ascherson. Ueber die Hautdriisen der Frosche. Arch. Anat. u 

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Bert, P. Venin cutane de la grenouille. C. R. Soc, Biol. (8), T. 2, 



1885. 



Biedermann, W. Zur Histologic und Physiologic der Schleimse- 

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Boulenger, G. A. The Poisonous Secretion of Batrachians. Nat. 

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Donaldson, H. H. On the Absorption of Water by Frogs. Science, 

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Drasch, 0. Beobachtungen an lebenden Driisen, etc. Arch. Anat. 

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Dutartre, A. Sur Ics changements de couleur chez la grenouille 

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Ehrmann, S. Zur Physiologic der Pigmentzellen. Cent. f. Phys., 



Bd. 5, 1891. 



Engelmann, T. W. Die Hautdrusen des Frosches. Arch, ges 



Phys., Bd. 5, 1872. 



