168 DR ALISON'S OBSERVATIONS ON 



pounds, but will aid and participate in the successive changes to which vegetable 

 matter is liable after the phenomena of its living state are over, and of which the 

 ultimate result is, the resolution of that matter into its original constituents. 

 And from these facts it seems quite reasonable to infer, that during the former, or 

 what we call the living state of the vegetable, certain aflBnities peculiar to the 

 living state — i. e., certain vital affinities — actuate the elements of which it is 

 composed. 



In asserting the existence of vital affinities, we do not, in the first instance, 

 give any opinion whether it is by the addition of certain chemical attractions, or 

 by the suspension of others, during the living state, that the chemical changes 

 peculiar to that state are effected ; we assert nothing more than what is, as I 

 think, correctly stated in the following sentence of Liebig : — " The chemical 

 forces in living bodies are subject to the invisible cause by which the forms of 

 organs are produced." " The chemical forces are subordinate to this cause of 

 life, just as they are to electricity, heat, mechanical motion, and friction. By 

 the inffiience of the latter forces, they suffer changes in their direction, an increase 

 or diminution of their intensity, or a complete cessation or reversal of their action. 



" Such an influence, and no other, is exercised by the vital principle over the 

 chemical forces." 



" The equilibrium in the chemical attractions of the constituents of the food 

 is disturbed by the vital principle, as we know it may be by many other causes. 

 The union of its elements, so as to produce new combinations and forms, 

 indicates the presence oi a peculiar mode of attraction, and the existence of a power 

 distinct from all other powers of nature, viz., the vital principle." — {Organic 

 Chemistry, ^c, pp. 355, 357). 



In these passages I think that Liebig has expressed himself with per- 

 fect accuracy ; but in other parts of his -s^Titings he uses language in regard 

 to the nature and results of chemical changes in living bodies, which seems to 

 me vague and speculative, and even inconsistent with what he had stated in the 

 passages just quoted, e. g., when he says that " the ultimate causes of the differ- 

 ent conditions of the vital force in nutrition, reproduction, muscular motion, &c., 

 are chemical forces^'' — {Organic Chemistry, p. 10). 



The following sentence by Mulder expresses the very same idea, although it 

 might be thought, from the manner in which this author expresses himself against 

 any introduction of the vital principle in this department of physiology, that he 

 considers all the chemical changes in living structm-es to be referable to the same 

 laws as in inorganic matter. 



" By a small organ of a plant a force is exercised, exciting forces which slum- 

 bered in the carbon, oxygen, and hydrogen, or rather modifying the forces which 

 existed in these, so that 12 equivalents of carbon unite with 10 of hydrogen and 

 10 of oxygen ; and from 12 equivalents of carbonic acid (12 C O^) and 10 of water 



