SURFACES 33 



in some mobile form, yet at the places where blood corpuscles are 

 formed it is chemically fixed as hemoglobin. We may say d priori 

 that the products of dissimilation become very soluble in the dispers- 

 ing medium, being dissolved or adsorbed but slightly by the dispersed 

 phase; in fact they are not chemically fixed at all, so that they leave 

 the body chiefly in the urine; they are, indeed, crystalloids of which 

 only so much is retained in the blood by solution or adsorption as is 

 necessary for a proper balance. 



We must here curtail our remarks and refer the reader to the 

 chapter on Distribution of Substances and Metabolism. 



What applies to the substances necessary for the maintenance of 

 the organism applies also to such foreign substances as have a toxic 

 or pharmacodynamic effect. It is a principle that such foreign 

 bodies as are chemically fixed, permanently injure the affected cell; 

 narcosis seems to me, to be a typical example of simple solution, 

 a process that is completely reversible. [Permanent injury may also 

 be caused by the breaking of an emulsion. See M. H. FISCHER and 

 MARIAN O. HOOKER, " Fats and Fatty Degeneration," John Wiley & 

 Sons, New York, 1917. Tr.] Between these extreme cases there are 

 substances which are adsorbed, and are active even in small doses, 

 though larger doses do not cause materially greater damage. Under 

 favorable conditions these processes may be reversible. The details 

 are treated of in the chapter on Toxicology and Pharmacology. 



Finally, I wish to refer to the chapter on Immunity Reactions 

 where it is an important question whether chemical combination, 

 solution or adsorption obtains. 



Surface Skins. 



Absolutely pure water has no surface viscidity, which means that 

 a metal or glass disc suspended by a thread at the surface performs 

 as many oscillations after a single turn as it does when immersed. 

 The slightest impurities may, however, suffice to cause a marked 

 retarding effect at the surface. On page 25 we saw that substances 

 which lower the surface tension of a fluid concentrate and spread 

 out at the surface, so it is to be expected that the surface will have 

 a different viscidity from the interior. POGGENDORFF and PLATEAU 

 were the first to study the formation of skins on fluids, but we are 

 indebted to M. V. METCALF,* G. NAGEL * and E. ROHDE * for recent 

 studies that have clarified the subject. It was shown as the result 

 of these investigations that colloids and substances at the border line 

 between colloids and crystalloids, especially many dyes, as fuchsin, 

 methyl violet, peptones and several other substances, concentrate at 



