LIFE. 



151 



soon as the living body has begun to chancre the 

 composition of the substances upon which it 

 acts, it endows them with a new set of affinities, 

 contrary to those which it before possessed 

 when subject to the operations of chemistry. 

 Others, again, are content to refer the opera- 

 tions in question at once to the ever-ready vital 

 principle, which, according to them, produces 

 and directs these changes in the organism, and, 

 so long as it resides there, keeps in check the 

 natural tendency of its structure to decay. We 

 are inclined to believe, on the other hand, that 

 the operations in question are immediately due 

 to the agency of the same laws as those which 

 preside over inorganic matter, operating, how- 

 ever, under conditions which the living or- 

 ganism alone can supply. We shall now 

 examine what evidence may be produced in 

 favour of this opinion, and how far it is con- 

 sistent with the general phenomena of life. 



V. CHANGES IN COMPOSITION. The ali- 

 mentary materials which serve as the food of 

 the living organism, cannot be appropriated by 

 its several tissues, and rendered like themselves 

 in structure and properties, until they have un- 

 dergone certain changes in composition, by 

 which the proximate principles are produced. 

 It is by the organisation of these compounds, 

 that the constant disintegration of the elemen- 

 tary parts of the living system is compensated, 

 and those vital properties maintained, the exer- 

 cise of which forms an essential part of the 

 circle of actions involved in life. Another 

 class of changes in composition consists in the 

 production, from the same materials, of the 

 peculiar ingredients which characterise each se- 

 creted product; some of these may be regarded 

 as directly eliminated from the nutritious in- 

 gredients of the blood, in the same manner as 

 are the solid tissues themselves; whilst others 

 would rather seem to result from the new com- 

 bination of the disintegrated elements, which 

 are taken up and removed by the current of the 

 circulation, and carried to organs destined to 

 separate them entirely from the living portions 

 of the system. All these changes are frequently 

 said to be effected by a vital chemistry ; or (to 

 speak in more precise language) to result from 

 the operation of vital affinities, of a different 

 character from those ordinary chemical affinities 

 which produce the well-known changes in the 

 inorganic world. In conformity with the New- 

 tonian direction to avoid unnecessarily multi- 

 plying causes;, we shall briefly examine the 

 grounds upon which this hypothesis is based, 

 and enquire whether it is requisite for the ex- 

 planation of phenomena, or even gives vis any 

 assistance in our researches. 



The chief ground for the assumption of a 

 distinct set of vital affinities appears to be, 

 that the mode of union of the elements of the 

 organic compounds is essentially different from 

 that which prevails in the inorganic world ; 

 and that the chemist, who has the power of 

 effecting or controlling those changes which are 

 produced by physical laws, and can therefore 

 imitate to a great extent the immense variety of 

 combinations which the mineral kingdom af- 

 fords, is unable to effect or control the action of 



similar materials, so as to produce any of the 

 class of organic compounds or proximate prin- 

 ciples. It has, until very recently, been re- 

 garded as a distinctive character of organic 

 compounds, that their elements are combined 

 in ternary or quaternary arrangements of com- 

 plex nature, in which each ingredient is equally 

 united with all the rest; whilst all inorganic 

 substances admit of being ultimately resolved 

 into simple binary combinations. Thus/zArira 

 is regarded as composed of 6 parts of carbon, 

 2 of oxygen, 5 of hydrogen, and 1 of nitrogen ; 

 and these elements are imagined to form a qua- 

 ternary compound, all having a mutual attraction 

 for each other ; whilst carbonate of ammonia, 

 which consists of 1 carbon, 2 oxygen, 3 hy- 

 drogen, and 1 nitrogen, is a binary combination 

 of two other binary compounds, carbonic acid 

 and ammonia. But on this it may be remarked, 

 that there are undoubtedly some proximate 

 principles, (that is to say, the simplest forms to 

 which organic compounds can be reduced, 

 without altogether disuniting them into their 

 ultimate elements,) which consist of two ele- 

 ments alone, and which exist in this simple 

 form in living bodies. Such are some of the 

 compounds of carbon and hydrogen. Further, 

 the rapid progress of analytic research is leading 

 to the belief that the complex arrangements 

 just referred to may be resolved into those of a 

 binary character; so that most organic com- 

 pounds may be regarded as resulting from the 

 union of others of simpler nature, just as a salt 

 is formed by the union of an acid and an alkali. 

 The discovery of cyanogen, and of its capabi- 

 lity of acting as a. compound radical, uniting, 

 like chlorine or iodine, with hydrogen to form 

 an acid, and even occasionally serving, like 

 oxygen or sulphur, in combination with some 

 metals, as the base or alkali to such an acid, 

 was the first step in a career of brilliant disco- 

 veries, which, even at the present day, may be 

 regarded as scarcely commenced. When cy- 

 anogen combines with a metal, the combination 

 is in reality a ternary one, although in all its 

 properties it has a binary character. Thus, the 

 cyanuret of silver (whose ultimate composition 

 is 1 part of the metal, with 2 carbon, and 1 

 nitrogen,) will form a salt, in which it acts as 

 the acid or negative ingredient, with the cya- 

 nuret of potassium ; and the soluble cyanurets 

 will form salts with the chlorides or iodides of 

 the metals, thus establishing their claim to a 

 binary character. But still further; cyanogen 

 in combination with iron appears itself to act 

 as a compound radical, combining as a simple 

 body with other elementary substances.* From 

 the analogy afforded by this and other in- 

 stances, many chemists are now disposed to 

 look upon the combination of the oxy-salts in 

 a new light. It is suspected that, vhen sul- 

 phuric acid and soda are brought together, the 

 resulting compound is not formed by the union 

 of an atom of the acid with an atom of the 

 alkali, but by the generation of a new com- 

 pound radical, sulphatoxygen, consisting of 1 

 part of sulphur with 4 of oxygen, which unites 



* Licbig, iii Turner's Chemistry, 6th cd. p. 776". 



