NATURAL SCIENCE IN THE NINETEENTH CENTURY 391 



ANATOMICAL AND MICROSCOPICAL SIMILARITY OF ANIMALS 

 AND PLANTS. ORGANS, TISSUES, CELLS, AND PROTOPLASMS. 

 The old cosmology emphasized differences rather than resem- 

 blances between animals and plants for, barring the one fact of 

 life, there is at first sight little in common between them. It 

 was always plain that both are provided with organs, and that in 

 respect to functions, such as growth, differentiation, the phases of 

 life and reproduction, there is great similarity. The improved 

 microscope of 1830-1850 now revealed a further and striking sim- 

 ilarity, by showing that the organs in both plants and animals 

 are made up of tissues, and these in turn of cells ; and when about 

 1845 it was found that both plant and animal cells contain a slimy, 

 colorless substance, apparently similar, if not actually identical, 

 in all living things, it was not long before the same name "proto- 

 plasm" (first life) was given to this fundamental substance, whether 

 it occurred in plant or in animal cells, in leaves or in muscles. 

 It was of this same fundamental protoplasm, common to both 

 plants and animals, that Huxley wrote his famous essay entitled 

 The Physical Basis of Life. 



FUNDAMENTAL UNITY OF NATURE. ORGANIC versus INORGANIC 

 WORLD. Between things organic and inorganic until the nine- 

 teenth century there was supposed to be a great gap. When, 

 therefore, in 1828 Wohler produced in the laboratory urea, a 

 typical organic substance hitherto unknown except as an animal 

 excretion, by merely heating ammonium cyanate, it became evi- 

 dent that in chemistry the term " organic " had lost its former 

 meaning. Since that time many compounds once believed to be 

 capable of production only by living things, have been made 

 in the laboratory, with the result that the organic and the inorganic 

 worlds have been drawn nearer together. The further fact that 

 living matter is composed largely of four common chemical 

 elements, carbon, hydrogen, oxygen, and nitrogen, and yields on 

 analysis no peculiar or mystical substance or element, tended to 

 show that life itself might be merely a property of various chemical 

 elements in peculiar combination. 



No less surprising than the revelation of the chemical similarity 



