Xiv INTEODUCTORY NOTE. 



Burdon Sanderson, Koch, and others. The union of 

 scientific minds is, or ought to be, organic. They are 

 parts of the same body, in which every member, under 

 penalty of atrophy and decay, must discharge its due 

 share of the duty imposed upon tlie whole. Of this 

 * body,' a short time since, England provided one of the 

 healthiest limbs ^ but round that limb legislation has 

 lately thrown a ligature, which threatens to damage 

 its circulation and to divert its energies into foreign 

 channels. In observational medicine one fine piece of 

 work may be here referred to — the masterly inquiry of 

 Dr. Thorne Thorne into the outbreak of typhoid fever 

 at Caterham and Eedhill. Hundreds were smitten by 

 this epidemic, and many died. The qualities of mind 

 illustrated in Dr. Thome's inquiry match those dis- 

 played by William Budd in his memorable investigation 

 of a similar outbreak in Devonshire. Dr. Budd's process 

 was centrifugal — tracing from a single case in the 

 village of North Tawton, the ravages of the fever far 

 and wide. Dr. Thome's proces's was centripetal — 

 tracing the epidemic backwards from the multitude of 

 cases first presented, to the single individual whose 

 infected excreta, poured into the well at Caterham, were 

 the cause of all. 



The Essays here presented to the reader belong to 

 the A B C of the great subject touched upon in the 

 foregoing Note. The two principal ones, namely. 

 Essays II. and III., were prepared for the Koyal 

 Society, and are published in the ' Philosophical Trans- 

 actions ' for 1876 and 1877. But, though written for 



