of the conservation of mass was thus established for living 

 matter also, and with the development of methods of 

 chemical analysis it was demonstrated that the living 

 organism was composed of the same elements as were 

 present in inorganic Nature. The energy changes going 

 on in plants and animals were found to obey the law of 

 energy conservation also. These facts made it seem rather 

 probable that living systems were in fact complex physico 

 — chemical ones, and the present-day view of most bi- 

 ologists is that the explanation of the function and struc- 

 ture of living things should be sought in terms of such 

 a picture. 



During the nineteenth century the first proof of the 

 minute structure of matter, and very important information 

 on the nature of light, was obtained. Dalton, in 1803, 

 gave the first scientific description of the structure of 

 matter when he showed that the known laws of chemical 

 combination could be explained, quite simply, by assuming 

 that all substances were composed of extremely small 

 particles — the atoms. The ancient Greeks had postulated 

 the existence of atoms to answer the question whether it 

 would be possible to continually subdivide any piece 

 of matter for ever, so that there would be an infinite num- 

 ber of pieces, or whether one would eventually arrive at 

 pieces which could not be further subdivided. The Greeks, 

 disliking the concept of infinity, concluded that matter was 

 atomic in nature, but they had no proof of this conclusion. 

 In his Atomic Theory, Dalton postulated as follows: 



(a) Every chemical element is composed entirely of atoms, 

 identical in size, mass, rigidity, etc. for any one ele- 

 ment, but different for different elements. 



(b) The atoms maintain their mass and individuality 

 in all chemical reactions in which they take part. 



49 



