52 BE JS NEXT, ON THE MOLECULAR THEORY, 



primarily owing to the successive formation of histogenetic and 

 histolytic molecules. We have already seen that develop- 

 ment and growth in animals originate in the molecules of 

 the yolk of the egg, or of a germinal molecular mass formed 

 from it. The author referred to numerous careful researches 

 recognised by scientific men as giving a correct account of 

 the development of various animals and textures. From these 

 it vrould appear that the first form was molecular ; that the 

 molecules united to produce nuclei and cells ; that these be- 

 came disintegrated to produce a secondary mass of molecules ; 

 that these again united to form secondary nuclei and cells ; 

 and that the same process was repeated more or less often in 

 various developments, until the animal or tissue was formed. 

 This constituted the successive histogenetic and histolytic 

 molecules observable in the process of growth — the former 

 building up, to a certain extent, and the product disintegra- 

 ting to produce the latter, which, after a time, again re-ar- 

 ranged itself and became histogenetic to form cells or tissues, 

 which in their turn broke down and became histolytic. In 

 short, not only development, but growth and secretion, ab- 

 sorption and excretion, were only different names given to 

 histogenetic and histolytic processes, and that these were 

 brought about by formative and disintegrative molecules. As 

 illustrations of this law, the author minutely followed the 

 development of Ascarix mystax, as descrilied by Nelson,'^ and 

 of the process of nutrition in the human body. 



In this, and a vast number of similar observations, it must 

 be evident that a certain series of molecular transfoinnations 

 is necessary for the one which follows it. Thereby is pro- 

 duced a continual elaboration of matter — a constant chemi- 

 cal and morphological series of changes — the exact number 

 and order of which, in the production of organic forms, only 

 requires time and perseverance to discover. Doubtless, various 

 conditions, dynamical, chemical, and vital, must co-operate 

 in producing the result, and they must all influence molecular 

 as well as every other kind of combination. Such considera- 

 tions and facts must convince us of the error of endeavouring 

 to place the source of special vital action in any particular 

 form or arrangement of organic matter, whether fibre, cell, 

 nucleus, or molecule. Each and all of these elements, the 

 author contended, had their vital endowments, which reope- 

 rate on the others. But, inasmuch as the molecular element 

 is the first as well as the last form which oraranized matter 



* 'Philosophical Transactions,' 1850, Plates xxviii, xxix, figs. 59, G8, 

 70, 78. 



