LIFE. 



153 



represented as constantly occurring in the tis- 

 sues, lias been unbalanced by the reposition of 

 nutrient materials ; and that it has therefore 

 manifested itself in the body even during life. 

 Again, when spontaneous gangrene occurs 

 from obstruction to the circulation, decomposi- 

 tion slowly supervenes in the part from which 

 the supply of nutrient fluid is cut off; and 

 coincident with its progress is the extinction of 

 the vital properties, constituting molecular 

 death. (See vol. i. p. 791.) Corresponding 

 changes may result in the whole body when 

 the nutritive functions are interrupted, not by 

 obstruction to the motion of the circulating 

 fluid, but by depravation of its character ; and 

 we then perceive the vital properties of each 

 tissue impaired in a degree correspondent to 

 the dependence of the integrity of its structure 

 upon the constant renewal of its elements. 



The presumed impossibility of forming, by 

 the chemical combination of their elements, 

 any of the class of organic compounds or prox- 

 imate, principles, is regarded by many physiolo- 

 gists as in itself a sufficient ground for the as- 

 sumption that the affinities which act in the 

 living body are different from those which we 

 recognize in the inorganic world. The fact, 

 however, which we have already noticed re- 

 garding the artificial production of urea is one 

 which powerfully opposes such an assump- 

 tion.* This is slurred over by Muller, with 

 the remark that it can scarcely be considered 

 as organic matter, being rather an excretion 

 than a component of the body a distinction 

 which does not remove it from the pale of the 

 operation of the supposed laws of vital affi- 

 nity. Seeing the vast progress which organic 

 chemistry has made during the last few years, 

 and the rapid increase of our knowledge re- 

 garding not merely the composition but the 

 mutual relations of the class of bodies under 

 consideration, we cannot but think it premature 

 to assert that other compounds may not be pro- 

 duced in a similar manner. Be it observed, 

 however, that the doctrine for which we are 

 now arguing only concerns the production of 

 those compounds which are destined either to 

 be thrown off from the system, or to undergo 

 subsequent organisation ; and cannot apply to 

 those in which the process of organisation, and 

 the consequent development of vital properties 

 have already commenced. This distinction is 

 a very important one, and may, we think, 

 by being kept steadily in view, save much un- 

 successful because mis-directed labour. If, for 

 example, our view be correct, it may be pos- 

 sible for the chemist to produce the gum or 

 sugar which he finds in the ascending sap of 

 plants ; but he can never hope to imitate the 

 latex or elaborated sap, which already shows 

 traces of organisation and of the possession of 

 vital properties. In like manner the formation 

 of albumen may be a worthy object of his 

 endeavours, whilst these would be totally fruit- 

 less if directed to the production of fibrin, 



* We do not quote any others reported to possess 

 the same character, such as the production of fatty 

 matter by Borard and Hatchett, because they still 

 require confirmation. 



which differs from it but littJe if at all in che- 

 mical constitution, but which is endowed in 

 its fluid state with properties that nothing but 

 the influence of a living system can generate. 



But quitting these speculations, we shall in- 

 quire what positive evidence niay be produced 

 of the operation of chemical affinities in the 

 changes of composition that form so important 

 a part of vital action. Many facts might be 

 collected which favour such a belief; but the 

 following must here suffice. In the progress 

 of vegetation we have frequent occasion to 

 observe the conversion of gum and of fecula, 

 which consists of gum enclosed in vesicles, 

 into sugar. This takes place in germination, 

 in the budding of the potato and other fleshy 

 stems, in flowering, in the ripening of fruit, as 

 well as in many other instances; in all these in 

 which fecula is the subject of the change, it 

 would seem that this product, having been 

 stored away out of the current of the circu- 

 lation against the time of need, is to be again 

 brought into use, and to supply the pabulum 

 of young or rapidly-growing parts by conver- 

 sion into sugar. These changes are effected ir 

 various modes. Where gum is the subject of 

 the conversion, we commonly find an acid 

 employed to produce it, as in the ripening of 

 fruits, where lignin as well as gum seems to 

 undergo this change. The chemist can pro- 

 duce the same effect by digesting gum or lignin 

 with an acid at a certain temperature. Again, 

 where the conversion of fecula into sugar takes 

 place as one of the ordinary processes of the 

 vegetable economy, it is effected by the pro- 

 duction of a secretion termed diastase, which 

 occasions both the rupture of the starch-vesicles 

 and the change of their contained gum into 

 sugar. This diastase, which is abundantly 

 stored up in the neighbourhood of the eyes or 

 buds of the potato, may be separately obtained 

 by the chemist; and it acts as effectually in his 

 laboratory as in that of the vegetable organism. 

 Further, he can imitate its effects by other che- 

 mical agents; for, by the joint operation of 

 heat and acid, he can produce the same trans- 

 formation. 



These are among the remarkable instances 

 of the catalytic action recently described by 

 Berzelius,* which is common to organic and 

 inorganic operations, and which is not yet 

 found to be comprehensible within the known 

 laws of chemical affinity. The peculiarity of 

 the action consists in the production by one 

 body, A, of a change in the composition of 

 another, B C, without itself undergoing any 

 alteration. Thus, the peroxide of hydrogen, 

 which is readily decomposed by any substance 

 having an affinity for oxygen, is also decom- 

 posed by some which themselves undergo no 

 change, such as the metals and the fibrin of the 

 blood ; these produce in it a state analogous to 

 fermentation, oxygen escaping and water being 

 left. Again, not only decompositions but new 

 combinations may be effected in this manner. 

 Thus, most metals at high temperatures, and 

 platinum in a state of minute division at low 

 temperatures, as well as various porous sub- 



* Edinb. Phil. Journal., vol, xxi. 



