44 THE POPULAR SCIENCE MONTHLY. 



But are we entitled from these facts to indulge in self-glorification, 

 and to assert that ultimately the exact reproduction of all the tissues 

 found in living organisms will be possible ? Certainly not, so far as 

 the chemist is concerned, for other methods than those which properly 

 belong to his science must obviously be sought to give the specialized 

 forms and functions of living substance. The gulf which separates 

 the artificial processes of synthetic chemistry from those really em- 

 ployed by the plant or animal is a wide one, across which lies as 

 yet no solid bridge of fact and theory. It is known that all vegetable 

 matter is derived primarily from carbonic acid, water, and ammonia, 

 under the influence of the sun's rays, but the method by which this 

 is done is still a mystery ; a mystery, though, which may be cleared 

 away, for very recently most interesting experiments have been made 

 on the chemical action of light. All we know about vegetable chem- 

 istry with certainty is, that, whatever are the processes occurring in 

 living tissue, most of them, in their earlier stages, are radically differ- 

 ent from those of art. In the laboratory, synthesis starts with the 

 elements, and from them, by exceedingly wasteful means, builds la- 

 boriously, from platform to platform, up to the desired height. On 

 the other hand, the smallest speck of green vegetable tissue, if living, 

 elaborates its substance, not from elementary bodies, but from com- 

 pound ones, and those too which are among the most stable and most 

 highly-oxidized known ; each new step, then, in the artificial method, 

 tends to carry us away, rather than to approximate us to the natural 

 agent. 



To return to the metaphor of the house. The chemist starts from 

 the ground, and completes the edifice by piling up^ one by one, the 

 elementary bricks, and binding them together by the natural cement 

 of atomic attraction. The living organism begins its labors at the top, 

 and chiefly from the three firmly-knit compounds, water, carbonic acid, 

 and ammonia, builds, by infinite gradation, down to an elementary 

 foundation ; and, at this day, science is scarcely more able to tell how 

 this is done, than can the mason inform us how to start a block of . 

 houses by commencing with the roof. 



This distinction as to methods includes obviously a vast domain 

 of facts, that which has been referred to as the region lying between 

 the natural and artificial synthetic methods. It is a sort of debatable 

 land, for, though it is yet unknown, there is not the slightest proof 

 that we shall not cross it some day, and possibly soon ; and already 

 the space is inhabited by speculations and embryonic theories, those 

 shadowy precursors of substantial knowledge. 



But the limit where the chemist must stop is the dividing line 

 where the naked individuality of a chemical compound becomes clothed 

 by the definite outline of an organ, a cell, or a speck of vitalized pro- 

 toplasm ; as soon as form other than crystalline appears, the sharpness 

 of atomic characteristics is merged in the idiosyncrasies of the cellular 



