404 PRINCIPLES OF CLASSIFICATION. 



to the more complex bodies, we have attempted to group together 

 substances presenting chemical similarities with those of equal 

 physiological importance. The deficiency of our knowledge on 

 many points to which allusion has frequently been made, must 

 plead as an apology for the deficiencies in our mode of arrange- 

 ment. The laborious accumulation of properties, which are only 

 slightly connected or are even altogether inapplicable, has grievously 

 oppressed the science of chemistry, and has reduced it to a mere 

 task of the memory. We have as yet no logical ideas in relation 

 to chemistry ; that is to say, although we have perfectly clear per- 

 ceptions regarding most bodies and processes, we have no distinct 

 ideas (in the logical sense). There is an utter absence of those 

 principles of unity around which, as around a nucleus, the indi- 

 vidual properties of bodies can crystallise, and thus stand in the 

 same mathemathical relation to one another, as the edges and angles 

 of crystal. 



It is not till chemistry shall have shown us the close mutual 

 connexion that exists between the properties of all individual sub- 

 stances, and shall have taught us to unite them into one organic 

 whole, that we can regard it as coequal in scientific rank with the 

 different branches of physics, that it will fully admit of the appli- 

 cation of the higher mathematics, or that the sole rational principle 

 of classification as well as a scientific theory of chemical substances 

 will be discovered. The beautiful investigations of Kolbe and 

 others regarding the numerical ratio existing between the densities 

 and boiling points of the haloid bases, the volatile acids, and the 

 haloid salts, as also the comparisons of the coefficients of density 

 of the constituent elements with the other properties of the com- 

 pound substance, may form a small beginning towards the attain- 

 ment of logical ideas and the realisation of such a degree of chemical 

 knowledge. When we have once attained logical ideas regarding 

 the different animal substrata, when we are in a position to foretell 

 the chemical properties of a body from its composition, or its com- 

 position from a certain number of its properties, we shall then not 

 only possess the true principle of classification in physiological 

 chemistry, but we shall also have attained the means of investi- 

 gating and comprehending the vital processes of nutrition and 

 secretion with a degree of certainty at present limited to the most 

 exact sciences. 



