WHAT IS A DISEASE? 413 



of the principal disease. Optic neuritis is the basis of a sub- 

 disease of tumour of the brain ; cirrhosis of the liver is the 

 basis of a sub-disease of alcoholism ; nephritis is the basis of 

 a sub-disease of scarlet fever, and so on. The principal disease 

 may subside, or its basis may be removed, and then it disap- 

 pears, leaving outstanding the sub-disease, which then becomes 

 the principal disease. 



2. A disease, then, is the whole group of correlated disorders 

 from which the patient suffers. If there is more than one 

 such correlated group, the patient suffers from more than one 

 disease ; but how if there is but one symptom, and this not 

 correlated with any assignable intra-corporeal cause ? What 

 is the nosological position of neuralgia, of asthma, of writer's 

 cramp, of diabetes insipidus, of dry mouth, wryneck, and 

 many other such disorders ? We call these diseases, but are 

 they rightly so called ? Each of them is but a single symptom, 

 uncorrelated with any other disorder, and due to no assign- 

 able cause. Are we justified in calling them diseases ? We 

 usually do call them diseases, but we do so with a certain 

 reservation and a shade of doubt. Each of them satisfies the 

 definition in as far as it is in the whole disorder from which 

 the patient suffers; but is it a correlated group of disorders ? 

 for that is the definition of a disease. I think it is. I think 

 that when we regard any of these disorders as a symptom, we 

 limit our contemplation of it to what we observe ; and we 

 observe but one thing — one uncorrelated disorder ; but when 

 we regard the disorder as a disease we do not so limit our 

 contemplation. 



3. In the first place, we should not regard as a disease a 

 single twinge of neuralgia, a single attack of asthma, a single 

 rigor, a single manifestation of writer's cramp, or epilepsy. Each 

 single attack or manifestation is a symptom only, or, if more 

 than a symptom, is certainly less than a disease. The disease 

 does not exist until the manifestation is repeated, for not 

 until there are two things to bring into relation with each 

 other can there be a correlation ; and it is the correlation, or 

 the group of correlatives, that constitutes the disease. In the 

 second place, when the manifestation is repeated, we do not 

 regard the repetition as fortuitous and accidental. We cannot 

 help supposing that the two or more manifestations are con- 

 nected together by some underlying cause or condition which 



