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 lo 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. 



REFERENCES 



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

 Phys., 1840. 



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

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Biedermann, W. Zur Histologic und Physiologic dcr Schleimse- 

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 Wien, 1887; Ueber den Farbenwechsel der Frosche. Arch. ges. Phys., 

 Bd. 51, 1892. 



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

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

 n.s.. Vol. 13, 1901. 



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

 u. Phys., phys. Abth., 1889. 



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

 commune {Nana esculenta). C. R. Hebdom. Ac. Sci., T. 3, 1890. 



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

 Bd. 5, 1891. 



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

 Phys., Bd. 5, 1872. 



