10 ORGANIZED BODIES. [iNTROD. 



This appears, from the interesting researches of Schleiden and 

 Schwann, to be the primary form which organic matter takes when 

 it passes from the condition of a proximate principle, to that of an 

 organized structure. 



The bodies of some animals and of some plants, are composed 

 almost entirely of cells of this kind ; and in the early development 

 of the embryo, all the tissues, however dissimilar from each other, 

 consist at first of nucleated cells, which are afterwards metamor- 

 phosed into the proper elements of the adult texture. 



An organized body possesses a definite form and disposition, not 

 only as regards its component parts, but likewise when viewed as 

 a whole. Each organized body has its appropriate and specific 

 shape; and to each a certain size is assigned. To observe and 

 classify the wonderful diversity of form exhibited by plants and 

 animals, has given employment to Naturalists in all ages; and 

 the sciences of Zoology and systematic Botany have been founded 

 upon the results of their labours. 



Every organized body is limited in its duration ; it has "its time 

 to be born and its time to die," and at death it passes by decom- 

 position into simpler and more stable combinations of the inorganic 

 elements. 



In their origin, organized bodies are generally, if not always, 

 derived from similar ones. Some have supposed that out of de- 

 caying vegetable or animal matter minute animals or plants of other 

 kinds may be formed : but it seems most probable that in those 

 cases in which they had been supposed to be formed, the seeds 

 or eggs, or even the parents themselves, had been concealed in 

 the decaying matter, or floated in the surrounding atmosphere. 

 Recent experiments throw considerable doubt upon this doctrine of 

 the spontaneous generation of organized bodies, by shewing that 

 neither vegetation nor the development of animalcule will go on 

 in fluids which have been subjected to such processes as must 

 inevitably kill whatever germs may have been diffused around or 

 throughout them. In the present state of our knowledge it may 

 be said, that the Harveian maxim, " Omne vivum ex ovo," is the 

 rule ; and that if there be any other mode in which the develop- 

 ment of living beings takes place, it is the exception. The progress 

 of Anatomical knowledge is every day revealing to us the organs, 

 and the mode of generation in the minutest and the least conspi- 

 cuous forms of vegetable and animal life ; and thus the doctrine, 

 which supposes that living objects may arise by a sort of conjunction 

 of the elements of decomposing organic matter, becomes more and 

 more improbable. 



