Augusi i8, 1881] 



NATURE 



371 



of preventible disease. It is the almost completely expressed 

 intention of our law th:it all such states of property and 

 all such modes of personal action or inaction as may be 

 of danger to the public health should be brought within 

 scope of summary pcocedure and prevention. Large powers 

 have been given to local authorities, and obligation expressly 

 imposed on them, as regards their respective districts, to 

 suppress all kinds of nuisance, and to provide all such works 

 and establishments as the public health primarily requires ; 

 while auxiliary powers have been given, for more or le.-s optional 

 exercise, in matters deemed of less than primary importance to 

 he.ilth ; as for baths and wash-houses, common lodging-houses, 

 labourers' lodging-house>, recreation-grounds, disinfection-places, 

 hospitals, dead-houses, burial-grounds, &c. And in the interests 

 of health the State has not only, as above, limited the freedom 

 of persons and property in certain common respects, it has 

 also intervened in many special relations. It has interfered 

 between parent and child, not only in imposing limitation on 

 industrial uses of children, but also to the extent of requiring that 

 children shall not be left unvaccinated. It has interfered between 

 employer and employed, to the extent of insisting, in the interest 

 of the latter, that certain sanitary claims shall Ije fulfilled in all 

 places of industrial occupation. It has interfered between vendor 

 and purchaser ; has put restrictions on the sale and purchase of 

 poisons ; has prohibited in certain cases certain commercial sup- 

 plies of water ; and has made it a public offence to sell adulte- 

 rated food or drink or medicine, or to offer for sale any meat 

 unfit for human food. Its care for the treatment of disease has 

 not been unconditionally limited to treating at the public expense 

 such sickness as may accompany destitution ; it has provided 

 that, in any sort of epidemic emergency, organised medical assist- 

 ance, not peculiarly for paupers, may be required of local 

 authorities ; and, in the same spirit, it requires that vaccination 

 at the public cost shall be given gratuitously to every claimant. 

 The above survey might easily be extended by referring to 

 statutes which are only of partial, or indirect, or subordinate 

 interest to human health ; but, such as it is, it shows beyond 

 question that the Legislature regards the health of the people as 

 an interest not less national than personal, and has intended to 

 guard it with all practicable securities against trespasses, 

 casualties, neglects, and frauds."^ At the time when that 

 description was written I unfortunately had to confess that the 

 intentions of the Legislature were not carried into effect ; for 

 that the then existing laws (especially in respect of the local 

 authorities which should give effect to them) were in a state of 

 almost chaotic confusion and unworkability ; but since that 

 time an entirely new constitution of local authorities has been 

 made, some thousands of additional officers have been appointed, 

 and the general fabric of the law has been consolidated, and its 

 powers in some respects extended and made more stringent, w ith 

 a view to the better prevention of disease, so far as legal powers 

 and facilities can attain that object. 



Such being the very large contribution which the Body-Politic 

 makes to the purposes of State Medicuie in this country, let us 

 next see how we of the medical profession stand in respect of 

 the scientific contribution which we distinctively owe to the same 

 great object. 



In preventive, just as in curative, medicine, it occasionally 

 hajipens that consequences more or less valuable result from 

 some mere chance-hit of discovery ; but except so far as this may 

 sometimes (and but very rarely) happen, disease can only be 

 prevented by those who have knowledge of its causts — know- 

 ledge which does not deserve to be called knowledge, unless 

 in proportion as it is conclusive and exact; and thoroughly 

 to investigate the causes and their mode of operation is the 

 quite indispensable first step towards any scientific study of 

 prevention. Essentially we know how to prevent, by having 

 first learnt exactly how to cause. Therefore it is that preventive 

 medicine has had almost no development until within these later 

 times. The germinal thought of it may be traced in even the 

 first days of our profession. The spirit in regard of which 

 Hippocrates has been aptly called the Father of Medicine — the 

 scientific spirit of observation and experiment, as distinguished 

 from the spirit of priestcraft, was one which his medical writings 

 equally showed in their preventive as in their curative relations ; 

 and when he, some twenty-three centuries ago, expounded to his 

 contemporaries that pathology is a branch of the science of 

 nature — that causes of disease are to be found in physical acci- 



^ '• Eleventh Report of the Medical Officer of the Privy Council," 1869, 

 pp. 20, 21. 



dents of air and earth and water, and In quantities and qualities 

 of food, and in personal habits of life, he (not without risk of 

 being denounced for impiety) virtually proclaimed for all time 

 the first principle of preventive medicine, and indicated to his 

 followers a new line of departure for those who would most 

 largely benefit mankind. His followers, however, have had 

 their work to do. True knowledge of morbific causes could 

 only come by vtry slow degrees, and as part of the development 

 with which the physical and biological sciences have, little by 

 little, with the labour of ages, been building themselves up ; and 

 so no wonder that, despite the lapse of time, even the most 

 advanced of nations are hitherto but beginning to take true 

 measure of the help w hich preventive medicine can render them. 

 Now what is the nature of that sludy of causes through which 

 we may gradually arrive at counter-causing or prevention ? 



Addressing a skilled audience, I shall utter what to them is 

 the merest commonplace when I say that, in the physical and 

 biological sciences we acknowledge no other study of causes 

 than that which consists in experiment. And the study of 

 morbific causes is no exception to that rule : it is solely by 

 means of experiment that we can hope so to learn the causes of 

 disease as to become possessed of resources for preventing 

 disease. 



The experiments which give us our teaching with regard to the 

 causes of disease are of two sorts : on the one hand we have the 

 carefully pre-arranged and comparatively few experiments which 

 are done by us in our pathological laboratories, and for the most 

 part on other animals than man ; on the other hand, we have the 

 experiments which accident does for us, and, above all, the 

 incalculably large amount of crude experiment which is popu- 

 larly done by man on man under our present ordinary conditions 

 of social life, and which gives us its results for our interpreta- 

 tion. 



When I say that experiments of those two sorts are the sources 

 from which we learn to know the causes of disease, I of course 

 do not mean that the mental process by which an experiment 

 becomes instructive to us is the same in regard of the two sorts 

 of experiment. On the contrary, the astiological problem (so 

 long as it is a problem) is approached in the two cases from two 

 opposite points of view ; and the dynamical continuity of rela- 

 tion, which we call cause and effect, is traced, in the one case, 

 from the one pole, and in the other case, from the other pole of 

 the relation. In the one case, starting with knowledge of our 

 own deliberately-prepared cause, our question is, What will be 

 its effect? In the other case, starting from a certain effect pre- 

 sented to us, our question is, What has'been its cause ? But in 

 the second case, just as in the first, when the question is 

 answered, when the problem is solved, when the relation of 

 cause-and-effect has been made clear, we recognise that the con- 

 jurmg-power which has brought us our new know ledge is the 

 power of a performed experiment. 



Let me illustrate my argument by showing you the two pro- 

 cesses at work in identical provinces of subject-matter. — What 

 are the classical experiments to which we habitually refer when 

 we think of guarding against the dangers of Asiatic cholera? 

 On the one side there are the well-known scientific infection- 

 experiments of Prof. Thiersch, and others following him, per- 

 formed on a certain number of mice. On the other hand, there 

 are the equally well-known popular experiments which, during 

 our two cholera epidemics of 1S48-9 and 1853-4, were performed 

 on half a million of human beings, dwelling in the southern dis- 

 tricts of London, by certain commerci.il companies which supplied 

 those districts with water. Both the professor and the companies 

 gave us valuable experimental teaching as to the manner in which 

 cholera is spread. I need not state at length the facts of _ those 

 experiments, probably known to all here, but may rather justify 

 my parallel by referring to an .etiological question which will 

 presently be discussed in our section. 



It concerns the causation of tubercle — the most fatal by far of 

 all the diseases to which the population of this ccuntry is subject. 

 On that subject, for the last sixteen years, we have had a new 

 era of knowledge. It was the great merit of a Frenchman, M. 

 Villemin, that he, in 1S65, first made us fully aware that tubercle 

 is an infectious disease. He did this by certain laboratory 

 experiments performed on other animals than man. He found 

 that general and fatal tubercular infection of the auimal was 

 produced when he inoculated it subcutaneously with a little 

 crude tubercular matter from the human subject. That first 

 laboratory investigation of the subject has been followed most 

 extensively by others ; and the further experiments, while 



