1032 Dynamic Theory. 



ance of the ordinary state of the ether of the tissues beginning at the 



surface of the skin and the taste papillae respectively. 



Cliemism and Ether. The theory of chemical attraction is not yet 

 settled, and there are various opinions. The opinion expressed in 

 Cooke's chemistry is that the atoms or molecules of the elements are 

 polar, in much the same way as metals and other bodies are magnetic 

 or electric. With some molecules the polarity is inherent and perma- 

 nent, and with others it can only be induced by causes outside of them- 

 selves. The last, answer to bodies called neutral in respect to electrical 

 attraction. Steel can be made into a permanent magnet, iron cannot. 

 But if polarity is induced in iron by the steel magnet, it becomes a mag- 

 net while under this influence of the steel, but ceases to be one as soon 

 as such influence is withdrawn. In like manner Prof. Cooke supposes 

 the action of chemical polarity is inherent in some bodies, and induced 

 in others. "Again, different substances are susceptible to chemical 

 polarity to very different degrees, and the susceptibilit}" varies under 

 different conditions. The chemical activity of a substance then depends 

 on the degree of polarity inherent in its molecules. The active quali- 

 ties of acids and alkalies show their molecules to be strongly polarized, 

 while the inert character of most elementary substances is explained by 

 the neutral condition which their homogeneous structures would natur- 

 ally produce in their molecules. For example, suppose ever}' molecule 

 of sulphuric acid, H 2 S0 4 , or of hydrochloric acid, HC1, or of sodic 

 hydrate, NaOH, is naturally polarized, while on the other hand the 

 molecules of zinc, Zn, magnesium, Mg, hydrogen, H-H, and of oxygen, 

 O-O, are normally neutral. As soon, however, as we place zinc in con- 

 tact with dilute sulphuric acid, the metallic molecules become polarized 

 by induction to the degree of which they are susceptible under the in- 

 fluence of this acid. A powerful attraction is thus developed in which 

 the familiar chemical action is the result. If magnesium is treated in a 

 similar way the action is more energetic because, as we suppose, the 

 molecules of this metal are susceptible to a higher degree of polarity, 

 and the force developed is proportionally stronger. On the other hand, 

 with metallic copper, there is no action under the same conditions be- 

 cause the molecules of the "metal do not acquire a sufficient degree of 

 of polarity to determine chemical change. " 



Atoms of the different elementary substances are recognized by chem- 

 ists as possessing a different number of points of union or poles, by 

 which they are attached to other atoms. These points are called bonds, 

 and the atoms possess these bonds from one to seven or eight in num- 

 ber. Atoms are classified according to the number of their bonds, and 

 graphically shown in figure 403. The names, from the Greek, signify 

 numbers which allude to the bonds or poles. 



