26 THE CAUSATION OF DISEASE. 



through the agency of a tissue (viz., the nervous) not sharing 

 in actual diseased action. Although it is now the fashion 

 to narrow the sphere of cold as a cause of disease, none, I 

 imagine, deny that it is adequate to cause ordinary croupous 

 pneumonia. This it probably does through the agency ot the 

 nervous system ; the external-mal-E acting upon the nervous 

 system of the lungs leads in them to a mal-environment, and 

 it is a -primary mal-environment, for we may presume that 

 no actual disease is set up in the nervous system, though 

 through it another tissue is morbidly affected. Some may think 

 I have not chosen a happy example in pneumonia, and they 

 may say the lung-trouble is a local expression of a general dis- 

 order. Be this as it may, the case, as I have put it, illustrates 

 my meaning. 



I have said that when a disease has a local beginning, it 

 should be our business to fix upon the tissue first affected, and 

 to trace all the resulting ill- consequences link by link. This 

 we do by a careful study of the morbid symptoms — past and 

 present — and of the external-body-environment. What are 

 the symptoms of disease ? They are the morbid changes which 

 show themselves during life either subjectively to the patient, 

 or objectively to him or to the examiner.* Yellow skin, itching, 

 &c. &c, are symptoms of obstructive jaundice ; uraemia, bron- 

 chitis, and hemiplegia, of granular kidney. All these symptoms, 

 be it noted, are due to secondary mal-environment, and, indeed, 

 most symptoms have a like origin. A feeling of weight 

 and pain in the chest from the ingestion of indigestible 

 food is apparently a symptom due to a primary mal-environ- 

 ment of the stomach's interior, but it is really due to a 

 secondary mal-E in the sensorium : impulses starting in the 

 gastric mucous membrane travel up to the sensorium, and set 

 up in it those mysterious changes which, in psycho-physiological 

 language, we are pleased to term the physical side of con- 

 sciousness. Almost all pains — the most terrible symptoms of 

 disease — are due to mischief outside the sensorium, for it is a 

 curious fact that disease of the cerebral grey matter generally 



* It is wise to make no distinction between signs and symptoms, for such a 

 distinction is both useless and confusing. 



