416 SCIENTIFIC THOUGHT. 



and development. Let us see how they affected biology 

 proper — the study of life. 



The early propounders of the cellular theory were 

 evidently much influenced by the then existing theories 

 which explained the constitution of inorganic chemical 

 substances by atoms and by the processes of crystal- 

 lisation. The progress of science, however, was in the 

 direction of showing more and more that these borrowed 

 conceptions are quite inadequate. Eeasoning or thinking 

 on organised matter is quite different from that which 

 refers to unorganised substance. Chemists and physicists 

 deal with atoms as imaginary units, which form the ideal 

 groundwork for constant arithmetical proportions or for 

 the action of calculable mechanical forces measured 

 by observable movements. Biologists, whether dealing 

 with plants or animals, approach the cells which they 

 regard as the units of living matter with the micro- 

 scope — an instrument which, till quite recently, has only 

 been sparingly used in chemical research. The units 

 of the chemist far transcend our powers of vision ; the 

 units of the biologist are to some extent accessible to 

 our senses. All organisms have been found to be 

 analysable by the aid of the microscope into similar 

 morphological constituents called cells, which present 

 very similar forms and functions. This has had the 

 advantage of permitting the phenomena of life to be 

 analysed into a few fundamental processes common to 

 all living things ; the great diversity of the larger 

 organisms, and the more conspicuous phenomena of life, 

 being conceived as put together in various ways out of 

 these elementary units, which exhibit in varying degrees 



