126 Proceedings of the Royal Physical Society. 
the standpoint of individual cellular physiology, and it is 
therefore necessary to commence with a definition of the 
terms “individual” and “ cell.” 
An individual I consider to be any inorganic or organic 
substance, or group of substances, capable of maintaining 
—under definite conditions—its specific character. The 
organic individual differs from the inorganic one in having 
a composition which allows it not only to maintain its 
specific character under the environmental conditions which 
gave rise to its existence, but which also enables it to react on 
the environment in such a way that the latter, by an unbroken 
chain of fermentative actions, is made to pass into higher 
and higher compounds. Such compounds will ultimately, 
according to their specific chemical constitutions and affinities, 
give rise collectively to the different kinds of organisms. 
This may be stated in other words, as follows:—The 
difference between an inorganic and an organic individual is 
simply this: in the former, the chemical affinity between cer- 
tain elements, or groups of elements, has been satisfied, and has 
come to a standstill; in the organic individual new chemical 
affinities are constantly being formed, to satisfy which the 
organism, be it plant or animal, requires to take up food. I 
look upon organic existence, with all its concurrent pheno- 
mena, as the result of hunger, and hunger I have, in a previous 
paper, defined as “an unsatisfied affinity of one element or a 
eroup of elements for another element or group of elements.” 
Such an organic individual is known to us in its simplest 
form as a unicellular being, which may be on a comparatively 
low grade of evolution, as the Amceba, or highly evolved, as 
the Infusoria, as examples of the latter I need only mention 
Paramecium and Vorticella, with their cilia, oral aperture, 
and complicated process of conjugation. But whatever be 
the degree of evolution which a unicellar plant (protophyton) 
or a unicellular animal (protozoon) may have reached, we 
can always make out a differentiation of the living organic 
matter or plasm (protoplasm) into a number of “organs,” each 
of which has to fulfil definite functions. 
1 Gustav Mann, The Embryo-sac of Myosurus—Trans. Bot. Soc, Edin., 
1892, pp. 351-428. 
