466 THE POPULAR SCIENCE MONTHLY. 



tend beyond all reasonable limits this Introductory Note. On the old 

 Baconian lines of observation and experiment the work is carried on. 

 The intercommunication of scientific thought plays here a most im- 

 portant part. It will probably have been noticed that, while physiol- 

 ogists and physicians in England and elsewhere were drawing copiously 

 from the store of facts furnished by the researches of Pasteur, that 

 admirable investigator long kept himself clear of physiology and 

 medicine. There is, indeed, reason to believe that he was spurred on 

 to his most recent achievements by the papers of 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 the 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 observa- 

 tional medicine one fine piece of work may be here referred to the mas- 

 terly inquiry of Dr. Thorne Thorne into the outbreak of typhoid fever 

 at Caterham and Redhill. Hundreds were smitten by this epidemic, and 

 many died. The qualities of mind illustrated in Dr. Thome's inquiry 

 match those displayed by William Budd in his memorable investiga- 

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

 centrifugal tracing from a single case, in the village of North Taw- 

 ton, the ravages of the fever far and wide. Dr. Thome's process was 

 centripetal tracing the epidemic backward, 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 Royal Society, 

 and are published in the " Philosophical Transactions " for 1876 and 

 1877. But, though written for that learned body, I sought to render 

 their style and logic so clear as to render them accessible to any fairly 

 cultivated mind. The essays on " Fermentation " and " Spontaneous 

 Generation " have already appeared elsewhere ; while the first essay, 

 on " Dust and Disease," has been for some years before the public. It 

 may be regarded as a kind of popular introduction to the more strenu- 

 ous and original labors which follow it. 



The essay most likely to try the reader's patience is Number III. 

 On the whole, however, and particularly in its bearings on the germ 

 theory of disease, it is probably the most important of all. The diffi- 

 culties which sometimes beset the experimenter in these investigations 

 are best illustrated by this essay. It shows, to my mind in a very 

 impressive manner, the analogy of the spread of infection among or- 

 ganic infusions with its mode of propagation among human beings. 



