3O ANIMAL CHEMISTRY LECTURE II. 



small, pertaining to ammonia. The residues are not intermingled 

 promiscuously, but remain apart, ever mindful of their distinct 

 individualities, ever longing to re-form the complete and separate 

 molecules from which they sprung. 



(28.) The progress of organic chemistry, then, has led to the 

 conclusion that highly complex molecules are built up of the 

 residues of less complex molecules, which constituent residues, 

 by a direct or indirect absorption of water, are capable of sepa- 

 ration from one another, and reproduction in their isolated and 

 perfect state. Accordingly, we regard highly complex or poly- 

 merone bodies as compounds formed by the union of less complex 

 or aplone bodies with one another, the union being attended by 

 an elimination of water. Now, these aplone molecules, of which 

 our constituent residues represent greater or less portions, are 

 found either to have a very simple constitution, or to be asso- 

 ciated with bodies of a very simple constitution, as members of 

 one and the same organic family. Despite their enormous 

 number, the great majority of them have been already referred 

 to certain definite positions in certain very simple groups and 

 series ; and we have every reason to believe that, with increase 

 of knowledge, they will all be referred in a similar manner to 

 groups and series, such as these to which I am pointing. Organic 

 chemistry, then, has achieved this great analytic success. The 

 compounds so elaborately built up by living organisms, it has 

 taken to pieces, and the pieces themselves it has arranged into 

 natural series and groups of associated bodies into series of 

 bodies of similar constitution and similar properties that are 

 not susceptible of mutual metamorphosis, and into groups of 

 bodies of dissimilar constitution and dissimilar properties that 

 are susceptible of mutual metamorphosis. 



(29.) Here, for example, we have a series of bodies, namely, 

 the primary monobasic fatty acids, beginning with formic acid 

 CH 2 O 2 , and ending for the present, at any rate, with melissic 

 acid, C 30 Il6o0 2 . Some of these acids have, as you perceive, a 

 very simple, others a somewhat complex constitution, but all of 

 them present an .obvious similarity of constitution, manifest the 



