8o PROTOPLASMIC ACTION AND NERVOUS ACTION 



type of specific growth and form-determination — similar 

 processes are almost certainly concerned. 



The reversible character of many adsorption processes 

 is a property of great biological importance and appar- 

 ently one essential to certain physiological effects, such 

 as narcosis, which are universal in living protoplasm. 

 There is no doubt that this reversibility also plays an 

 essential part in the normal chemical processes of proto- 

 plasm. The displacement of one adsorbed compound by 

 another of greater surface-activity presupposes reversible 

 adsorption, and various biological instances of this effect 

 are known. Thus an adsorbed enzyme can be removed 

 from an adsorbing surface by adding a more surface- 

 active substance; e.g., rennin adsorbed by charcoal and 

 added to milk will not coagulate the latter, but on the 

 addition of saponin the rennin is set free and causes 

 coagulation. A solution of rennin is inactivated by 

 shaking with air, but not if saponin is present; the latter 

 protects the enzyme by preventing adsorption at the 

 air-water interface.' 



Similar cases of inactivation by shaking are cited 

 by Meltzer and Shaklee.^ Apparently only the adsorbed 

 enzyme is inactivated; it has already been mentioned 

 that changes of physical state frequently result from ad- 

 sorption; Ramsden's observation that proteins can be 

 coagulated by shaking with air is an instance of the same 

 phenomenon.^ Hence the prevention of adsorption 

 through the presence of another surface-active com- 



*Cf. the observations of Jahnson-Blom (1912), and Schmidt- 

 Neilson (1910), cited in Bayliss' Principles of General Physiology, p. 70. 



* Meltzer and Shaklee, Amer. Jour. Physiology, XXV (1909), 81. 



3 Ramsden, Z. physik. Chem., XL VII (1904), 343. 



