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 

 tinder pressure depends also upon the direction of flow. 

 Cima found that as much water under a pressure of 10 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 

 Phys., 1840. 



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

 1885. 



Biedermann, W. Zur Histologie und Physiologic der Schleimse- 

 cretion. Sitzb. d. k. Ak. Wiss. Math.-nat. Cl., Bd. 94, Abth. 3, 1886, 

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

 Bd. 51, 1892. 



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

 Sci., Vol. i, 1892. 



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 {Rana 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 Hautdriisen des Frosches. Arch, ges 

 Ph s., Bd. 5, 1872. 



