176 THE CAUSATION OF DISEASE. 



And being thus an aberrant or abnormal mode of life, it is 

 advisable, in seeking the material conditions out of which dis- 

 ease arises, to first ask the question, What are the material 

 conditions out of which life arises ? 



To speak first of unicellular organisms. We may say that 

 the immediate causation of life in such = ' ' the material con- 

 ditions as constituted by the cell plus all those material con- 

 ditions of the cell-environment which take part in the vital 

 inter-action." The causation of life in such an organism may 

 be therefore represented by the formula, S -f E. 



If S be properly constructed, and if the E be fit, the vital 

 processes go on in orderly fashion ; but if either the one or 

 the other be unfit, an abnormal inter-action occurs, and this is 

 disease. Disease, being thus an abnormal inter-action of S and 

 E, must be caused by some fault in S, in E, or in both. 



We have, therefore, in investigating the causes of disease, to 

 inquire most carefully into the material conditions of S and E. 

 We cannot state these exactly, even in the case of unicellular 

 organisms ; for who will engage to define accurately the mate- 

 rial conditions of a unicellular organism — to specify the exact 

 relations of atom to atom in the molecule, of the molecules 

 among themselves, or the precise movements whereby either is 

 agitated ? Our knowledge of the material conditions of the 

 cell is, in fact, limited to its microscopic characters and 

 chemical composition, and even in these respects it is very 

 inadequate. The same is true of the cell-E, the exact material 

 conditions of which we can by no means state accurately. 



But although it is impossible, even in the case of unicellular 

 organisms, to specify in minute detail the material conditions 

 out of which the vital processes arise, this should, nevertheless, 

 be our aim, if we wish to discover the cause of life, and the 

 more accurately we can define these material conditions, the 

 more complete will be our knowledge of vital causation, be 

 it physiological or pathological. 



The Environment. — The internal-cell-E. — In multicellular 

 organs, the E falls into a twofold division, into (a) the internal- 

 cell-E and (b) the external-body-E. The life of such an 

 organism may be defined as the " sum of the inter-actions of 



