CONCLUDING REMARKS. 217 



wonderful simplicity of the means or the forces by which the world 

 of external phenomena is maintained in a state of incomprehensible 

 alternation. There are only three groups of organic substances 

 through which all the vital phenomena are manifested, and even 

 these groups exhibit the most important internal co-relations. 

 May we not conjecture, although we are still unable to prove the 

 fact, that members of the group of fats may be formed, like those 

 of the group of carbo-hydrates, from histogenetic bodies ? And do 

 not the members of the individual groups present such uniformity 

 and analogy in their composition, and even in their properties, 

 that the diversity of the processes to which they give rise is per- 

 fectly incomprehensible ? We are thus obliged to have recourse to 

 isomerism and polymorphism as a prop to our ignorance, and as 

 the means of affording us at least some clue to the manner in 

 which protein-bodies, which appear almost identical, can be 

 exhibited under such numerous modifications of form, and can so 

 variously influence the mechanism of the living organism. There 

 are almost inappreciably small differences in the composition and 

 qualities of the substances which, as far as we know, are most 

 homologous with ethereal bodies, viz., the fatty substances ; yet 

 the different fats do not produce the same or even analogous effects 

 in the animal body. The carbo hydrates, which to a superficial 

 observer might seem to be destined solely to undergo disintegration 

 in the animal body, exhibit the most various metamorphoses and 

 subdivisions before they are fitted to perform their part beneficially 

 in the apparent intricacy of the vital phenomena. Potash and 

 soda, for instance, are substances which the chemist finds it 

 extremely difficult to keep asunder in his systems, and which 

 frequently appear to replace one another in the mineral kingdom ; 

 yet they are employed in life to maintain the most strikingly op- 

 posite conditions ; whilst carbonic acid, the weakest and most 

 volatile of all acids, is occasionally made to perform the same 

 service in the organism as the powerful and solid phosphoric 

 acid. 



It might here be asked whether nature has not employed 

 forces peculiar to itself in regulating, with these few means, the 

 internal economy of animal life, while we are admiring the insig- 

 nificant expenditure of force which is required to convert these 

 changeable bodies from one form to another. When we see how 

 readily the largest quantities of starch or cane-sugar are converted 

 into grape-sugar by almost inappreciable quantities of diastase or 



