312 THE CAUSATION OF DISEASE. 



nervous system, for E being normal, and disease depending 

 npon an inter-action of S and E, S must be abnormal. 



In such cases the structurally deficient tissue may be 

 limited, and the abnormality may possibly be so subtle as to 

 be absolutely undiscoverable, but structural abnormality there 

 certainly is. This, it is obvious, from the definition of struc- 

 ture already given, may consist in peculiarity in respect of — 

 a, the arrangement of the atoms into molecules ; Z>, the dis- 

 position of these latter among themselves; c, the mutual 

 arrangement of the individual cells into tissues ; and, finally, 

 d, the mutual connection of physiologically distinct tissues. 

 Thus, in normal nerve centres there must not only be a proper 

 structure of individual cells, but also a. proper connection of 

 these by processes, or what not, into individual centres, and, 

 further, a proper connection between the individual centres 

 themselves. We can well understand how a nervous system 

 might be deficient in one of these particulars without our 

 being able to detect the deficiency by the most elaborate 

 search. 



A deficiency in any one or other of them constitutes 

 the lesion in this class of functional diseases, and it exists 

 before the actual disease is present. The exciting cause 

 of these pure neuroses leads to an exaggeration of the 

 abnormality, and the weakness is then suddenly revealed. 

 This sudden increase of abnormality is certainly of the nature 

 of molecular change ; its very suddenness, as well as the char- 

 acter of the exciting cause — e.g., strong emotion (which may 

 set up epilepsy, hysteria, neuralgia, or chorea), proves this. 

 A sudden emotion cannot induce alteration in the connections. 

 of cell with cell, or centre with centre ; it can only lead to an 

 atomic or molecular commotion. In these cases the centres 

 immediately affected may be very limited, but eventually, 

 owing to the mutual connection of tissue with tissue, a large 

 portion of the nervous system may become involved. 



It is worthy of note that the neurosis thus suddenly induced 

 may last a long time ; indeed, its effects may not wear off 

 for months. Seeing that disease = an abnormal inter-action 

 between S and E, it is conceivable that its continuance might be 

 due to a continuously-operating mal-E, the abnormality of S- 



