Chap, v.] CONSTITUTION OF OEGANISED BODIES. 37 



contains another cellulav element which is smaller, a nucleus in 

 which the living activity of the cell usually attains its mazimimi 

 of power. Moreover, it often happens, especially in plants, that 

 the exterior surface of the cellular corpuscle hardens. This 

 hardened surface then constitutes what is called the cellular 

 membrane. 



The observations and the inductions of palaeontology, of em- 

 bryology, of the systematic natural history of organised beings, 

 authorise us in considering the organic cell as the comer-stone 

 of the living world, the common mother of all other histological 

 elements. In eSect the first figurate living beings have been 

 monocellular, or composed of cells resembling each other, and 

 simply juxtaposed. At the origin of nearly the whole of living 

 beings, animals or plants, we find a simple cell. Finally, when 

 we hierarchically class the innumerable organised beings which 

 people our globe, we encounter, at the lowest, the humblest 

 degree, beings composed of a single cell, or of a small number 

 of identical and juxtaposed cells. 



The cellular theory which we have Just in summary fashion 

 sketched, is one of the grandest views of Biology. Bichat was 

 the first to attempt the anatomical analysis of living beings, by 

 trying to resolve each organised being into tissues anatomically 

 and physiologically special. Sphwann, carrying analysis further, 

 decomposed the tissues themselves into microscopical elements, 

 and was the first to formulate the cellular theory in Ms work 

 entitled Microscopical Researches on the Conformity of Structure 

 and of Growth of Animals and Plants. 1838. ^ 



The cellular theory contested at present, or rather differently 

 interpreted on certain points by M. Ch. Robin and his school, 

 nevertheless keeps its ground as a whole. It is not easy to 

 understand without it the genesis and^the evolution of organised 

 beings. Finally, this theory has led Physiology to scrutinise 



1 MikrOSkopiache Vntersuehungen iiier die UberemstwiMiung in der StruMur 

 vmd dem Wachsthum der Thiere imd Pflanzen. — ^De Mirbel had already shown 

 that the tissue of plants is composed of utricles and cells. 1831-1832. 



