96 PROXIMATE PRINCIPLES OF THE THIRD CLASS. 



the relative quantities of these elements vary within certain limits, 

 in different individuals and at different times, without modifying, in 

 any essential degree, the peculiar properties of the animal matters 

 which they constitute. This fact is altogether a special one, and 

 characteristic of organic substances. No substance having a definite 

 chemical composition, like phosphate of lime, starch, or olein, can 

 suffer the slightest change in its ultimate constitution without being, 

 by that fact alone, totally altered in its essential properties. If 

 phosphate of lime, for example, were to lose one or two equivalents 

 of oxygen, an entire destruction of the salt would necessarily result, 

 and it would cease to be phosphate of lime. For its properties as a 

 salt depend entirely upon its ultimate chemical constitution ; and if 

 the latter be changed in any way, the former are necessarily lost. 



But the properties which distinguish the organic substances, and 

 which make them important as ingredients of the body, do not 

 depend immediately upon their ultimate chemical constitution, and 

 are of a peculiar character ; being such as are only manifested in 

 the interior of the living organism. Albumen, therefore, though 

 it may contain a few equivalents more or less of oxygen or nitrogen, 

 does not on that account cease to be albumen, so long as it retains 

 its fluidity and its aptitude for undergoing the processes of absorp- 

 tion and transformation, which characterize it as an ingredient of 

 the living body. 



It is for this reason that considerable discrepancy has existed at 

 various times among chemists as to the real ultimate composition 

 of these substances, different experimenters often obtaining differ- 

 ent analytical results. This is not owing to any inaccuracy in the 

 analyses, but to the fact that the organic substance itself really has 

 a different ultimate constitution at different times. The most ap- 

 proved formula are those which have been established by Liebig 

 for the following substances : 



Fibrin = C 29 JI 228 N 40 92 S 2 



Albumen = C 2;6 H I69 N 27 68 S 2 



Casein = C, 88 H 228 N 36 90 S 2 



v Owing to the above mentioned variations, however, the same 

 degree of importance does not attach to the quantitative ultimate 

 analysis of an organic matter, as to that of other substances. 



This absence of a definite chemical constitution in the organic sub- 

 stances is undoubtedly connected with their incapacity for crystalli- 

 zation. It is also connected with another almost equally peculiar 

 fact, viz., that although the organic substances unite with acids and 



