NATURE OF DISEASE. 121 



diseases of the respiratory organs, of the absorp- 

 tive organs, and so forth, as opposed to local 

 lesions. 



Critical examination, however, shows that no 

 such distinctions can be consistently maintained, 

 I partly because the organs and functions of plants 

 are not so sharply marked off as they are in 

 animals, the diseases of which have suggested the 

 above classification, and partly because all dis- 

 ease originates in the cells and tissues, and it is a 

 matter of detail only that in some cases e.g. 

 severe freezing or drought of seedlings, or when 

 some ingredient is wanting in the soil the 

 diseased condition affects practically every cell 

 alike from the first, while in others it spreads 

 more or less rapidly from some one spot. 



Even the distinction into physiological diseases 

 versus parasitic diseases cannot be maintained 

 from the standpoint of the nature of the disease 

 itself All disease is physiological in so far as 

 it consists in disturbance of normal physiological 

 function, for pathology is merely abnormal 

 physiology, no matter how it is brought about. 

 This is not saying that no importance is to be 

 attached to the mode in which disease is in- 

 curred or induced : it is merely insisting on the 

 truth that the disease itself consists in the living 

 cell-substance the protoplasm not working nor- 

 mally as it does in health, and this, whether want 

 of water, minerals, or organic food be the cause, or 

 whether the presence of some poison or mechanical 

 irritant be the disturbing agent, as also whether 



