412 SCIENCE PROGRESS 



for their causation some special action from without, such as 

 the bite of an infected insect, faulty diet, cold, damp, or what 

 not ; but these are not parts of the disease. They do not enter 

 into our concept of the disease. They are causes of the disease, 

 but, being extra-corporeal, they are not parts of the disease. 



i . This concept of a disease needs some further qualification 

 before it can be accepted as complete and final. To recur 

 to the combination of rheumatism, heart disease, embolism : 

 these, as long as they co-exist, constitute, with their symptoms 

 and other consequences, a single disease. They constitute a 

 correlated group of disorders, structural and functional, all 

 assignable to a single intra-corporeal cause, the rheumatic 

 infection which correlates them and combines them into a 

 single group, contemplatible as an individual whole. Never- 

 theless, each of them has a certain separateness and individuality 

 of its own. The rheumatic infection may die out and disap- 

 pear, and then the disease is no longer rheumatism : it is now 

 heart disease complicated with embolism. Let us suppose 

 that the heart disease also recovers and its structural integrity 

 is restored : the disease is now embolism only. Or there 

 may have been no embolism, and on the disappearance of the 

 rheumatism the disease is heart disease only. Heart disease 

 and embolism may, therefore, in some cases be sole diseases, 

 complete diseases, separate diseases ; but when they co-exist 

 with each other, or with acute rheumatism, what is their 

 position ? Separate diseases they certainly are not, but may 

 not each be regarded as a disease, complete in itself ? In a 

 sense, yes : in a sense, no. Each is a complete disease in the 

 sense that it is a group of disorders correlated by a causal 

 structural change sufficient to account for them all ; but it 

 is clear that when associated together, or with rheumatism, 

 there is a further correlation, and thus our concept of the 

 disease from which the patient suffers is not complete until 

 they are all correlated into a single more comprehensive con- 

 cept. The whole disease from which the patient suffers is 

 rheumatism, complicated with heart disease and embolism ; 

 but these constitute subordinate correlations, which we may 

 appropriately term sub-diseases. Such sub-diseases are not 

 infrequent, and may be of such importance and danger to 

 life as to compel us to concentrate our attention upon them, 

 and to treat them, to the subordination, for the time being, 



