PROPERTIES 353 



enzymes the sensitiveness of an active enzyme, dissociated 

 from the living cell, to heat is most readily explained by at- 

 tributing it to the colloidal nature of the 'enzyme with the 

 consequent tendency to coagulation by heat. 



With regard to the action of light rays on enzymes it ap- 

 pears, according to lodlbauer and v. Tappeiner,* that there 

 exist two distinct kinds of action : 



(a) Those produced by ordinary light in the presence of 

 oxygen, and (#) those produced by ultra-violet light independ- 

 ently of oxygen. 



The destructive action which has resulted from exposure 

 to bright sunlight therefore appears to be dependent on the 

 presence of oxygen, and is greatly increased by the presence 

 of fluorescent substances, such as eosin, quinoline red, etc.f 



It was first shown by Green J that ultra-violet light de- 

 stroyed diastase, and since then several other authors have 

 described similar effects for other enzymes. 



The action of radium and radium emanation on enzymes 

 has been studied by WilcockJI by Loewenthal and Edelstein,1T 

 by Bickel, by Loewenthal and Wohlgemut, and others.** 



The influence of various chemicals on the activity of 

 enzymes will be dealt with later under the heading of 

 " paralysers ". 



COLLOIDAL NATURE OF ENZYMES. 



A fairly detailed account of the nature of colloidal solu- 

 tions has been given above ; it will suffice, therefore, merely 

 to mention here that enzymes possess most of the more im- 

 portant properties of such solutions. 



Foremost amongst these properties is their want of dif- 

 fusibility; as already pointed out, this does not mean that 

 they are quite unable to diffuse, but rather that their rate of 

 diffusion is very smallff Their ability to diffuse through a 

 membrane commonly known as dialysis is largely depen- 

 dent on the nature or structure of the membrane, but, as a 



* lodlbauer and v. Tappeiner : **Deut. Archiv. Klin. Med.," 1906. 



f Tappeiner : " Biochem. Zeit.," 1908, 8. 



$ Green: "Trans. Roy. Soc., Lond.," 1897, 188, 167. 



E.g. Burge, Fischer, and Neill : "Amer. Journ. Physiol.," 1916,40, 137, 

 426. 



HWilcock: "Journ. Physiol.," 1907, 34. 

 1F Loewenthal and Edelstein : " Bioch. Zeit.," 1908, 14, 484. 

 ** Loewenthal and Wohlgemut: id., 1909, 21, 476. 

 ftChodjajew: "Arch. Phys.," 1898, 241. 



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