266 APPENDIX A 



can be brought to show that known causes can produce 

 them. If so they can be classed. If they are unique 

 phenomena in infection they obviously cannot be classed. 

 But as overgrowth is not a unique phenomenon among 

 developmental diseases, and as we know that it can be 

 caused, or inhibited, by chemical cell-products, we are 

 entitled to declare that infection, if a cause, is a secondary 

 one, and that the real cause lies among the phenomena of 

 growth as much as acromegaly and other disorders due 

 to unregulated stimulation of organic tissues. 



It is impossible to argue clearly upon so complex a 

 subject unless the nature of explanation is really under- 

 stood. We need but ask any one to " explain " explana- 

 tion to find how few have clear ideas on the subject. 

 According to the logicians a partial comparison is not 

 explanation. The phenomena of one science are only to 

 be regarded as explained when they can be classed among 

 the observed sequences, or so-called laws, of a more 

 inclusive science. Therefore the pathological phenomena 

 of malignancy must be capable of classification with regard 

 to physiological phenomena as we must regard patho- 

 logical facts as deviations from the average or normal 

 tissue. In the paper I endeavoured to range the facts 

 under physiological and biological laws, since biology 

 includes physiology and pathology. However unsuc- 

 cessful the attempt may have been, it is obvious that it 

 was not made without reason or without results, whereas 

 the attempt to range them under the observed sequences 

 of bacteriology fails in vital particulars, and leaves us 

 just where we were, that is, in presence of a possible 

 infective agent which is hypothetically given the qualities 

 that produce the effects with none of the known signs of 

 infectivity. For until a malignant growth becomes really 



