34 THE CAUSATION OF DISEASE. 



another, the adaptive process will be constantly interfered 

 with. 



We have seen that the E differs not only for different 

 species of animals and for the different occupations of men, 

 but that it differs also for all individuals. This is evident on 

 the face of it, but it becomes doubly obvious when it is 

 remembered that the E even of no two unicellular organisms is 

 the same. Among a colony of such organisms inhabiting the 

 same medium, it might perhaps be thought that the E would 

 be the same for each. Nevertheless, as Herbert Spencer tells 

 us, it is utterly impossible for any two particles of matter, no 

 matter how microscopic, "to be similarly circumstanced in 

 respect of the incidence of external forces." And if this be 

 true of a unicellular organism, how much more must it be true 

 of a being whose constituent cells are to be counted by the 

 million ? 



Summary. — Here let us stop for a moment and survey our 

 present position. 



The various phenomena of Nature depend upon material 

 conditions, as defined. The same material conditions always 

 tend to the same results. 



The material conditions of a living protoplasmic cell — 

 which conditions are more or less perfectly embraced under the 

 term Structure — are such, that when it is placed amid certain 

 other material conditions, conveniently summed up under the 

 term Environment, an inter action takes place between cell and 

 environment. This inter-action is what we call Life, and the 

 sum of the inter-actions between any given cell and its en- 

 vironment constitutes the entire life of the cell. When these 

 inter-actions depart from a certain standard termed Health 

 ' — which no man has yet been able to define, but of which 

 our notion is sufficiently clear — we have Disease. Life, how- 

 ever, is still going on ; disease is, then, an altered mode of life, 

 an abnormal inter-action of S and E, depending on peculiarities 

 in either or both. It is, as Huxley says, a branch of biology. 

 In the complex organism, man, we depart from the simple 

 unit-cell, and we have, instead, to deal with millions of cells, 

 grouped into organs, and all knit into a physiological whole in 

 such a way that any one tissue is able to modify the E of 



