THE CAUSATION OF DISEASE. I 3 



structure {see fig. 1). (3) Finally, as I have already said, 

 differences in function are a distinct proof of differences in 

 structure. Think, for an instant, of an impregnated ovum 

 and of the vast potentialities locked up within it. There is 

 little difference between the apparent structure of a human 

 ovum and that of many belonging to the lower animals ; but 

 the fact that each develops into an entirely different being, 

 shows what a vast difference there must be in the minute 

 structure of each. One might be pardoned for lingering long 

 on a subject like this. Who, possessed of any imagination, can 

 think of the microscopic ovum-cell without feeling wonder? 

 It appears to consist of nothing but a very slightly differen- 

 tiated protoplasm ; but this is simply because our senses are 

 limited in scope, and are unable to take account of what we 

 may, somewhat paradoxically, term the vast world of the in- 

 finitesimal. The potentialities of the ovum are the outcome of 

 certain material conditions. In this tiny cell are aggregated 

 billions of atoms and molecules. These are arranged in 

 peculiar ways, and it is upon the nature of the atoms, the 

 arrangement of the atoms into molecules, and of these latter 

 among themselves, that the subsequent developmental changes 

 depend — just as the complex movements of the heavenly bodies 

 depend upon the nature (mass, &c.) of the individual heavenly 

 bodies, the arrangement of these into planetary systems, and 

 the relations of the planetary systems one to another. Thus 

 we may speak of the heavens as possessing an infinitely 

 complex structure, and thus also all analogy leads us to 

 assume that an ovum-cell, or indeed any other mass of 

 living protoplasm, is endowed with a structure so subtle and 

 intricate as to be out of the reach of man's limited faculties. 



I have thus far only spoken of the " structure "' of individual 

 cells ; but in considering this term as applied to living matter, 

 we must, in the case of multicellular organisms, include the 

 relations of cell to cell— that is to say, the grouping of cells 

 into tissues. It is in this latter sense that the term is more 

 ordinarily employed, but it appears to me to have a wider 

 scientific meaning : thus, I include under the word " Struc- 

 ture," as applied to living matter — (a) the mutual relations of 

 the constituent atoms in the molecules ; (b) the relative positions 



