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NATURE 



\August 1 8, 1 88 1 



entirely confirming M. Villemin's discovery, have shown that 

 subcutaneous inoculation is not the only mode by vvhicli tlie 

 tubercular infection can be propagated. Dr. Tappeiner and 

 others have shown that the same effect is produced on the 

 animal if tubercular matter (such as the sputa of phthi>ical 

 patients) he diffused in spray in the air which the animal breathes ; 

 and Prof. Gerlach of Hanover showed twelve years ago with 

 regard to the bovine variety of tubercular disease {the perlsucht 

 of the Germans), that its infection can be freely introduced 

 through the stomach if bits of tubercular organs be given in the 

 food, or if the healthy animal be fed with milk from the animal 

 which has tubercle. That the communicability of tubercle from 

 animal to animal is aho being tested to an immense extent by 

 popular experiments on the human subject, is what a moment's 

 reflection w ill tell ; and from that wide field of experiment I 

 select one instance for illustration. I have every rea-on to 

 believe that Prof. Gerlach's experiments on the communicability 

 of tubercle by means of milU are very extensively parodied by 

 commercial experiments on the human subject. I learn, on 

 what I believe to be the highest authority in this country, that 

 tubercle (in different degrees) is a malady which abounds among 

 our cows ; and that so long as the cow continues to give milk-, 

 no particular scruple seems to prevent a distribution of that milk 

 for popular use. To the persons who consume that milk an 

 important question as to the causability of tubercle is put in an 

 experimental form. Whether they will become infected with 

 tubercle is a que?tion which the imlividual consumers do not 

 stand forward to answer for themselves, like the animals of the 

 laboratory experiments : but Dr. Creighton's lately-published 

 book, entitled, "Bovine Tuberculosis in Man," and a paper in 

 which I am glad to say he brings under notice of our section the 

 very remarkable series of facts on which he grounds that start- 

 ling title, seem to suggest a first instalment of answer in accord- 

 ance with Prof. Gerlach's experimental finding. 



The two sorts of experiment — the scientific and the popular — 

 differ, as I have noted, in this particular : that the popular 

 experiment is almost always done on man ; the scientific aluiost 

 always on some other animal. It is true that many memorable 

 cases are on record, where members of our profession have de- 

 liberately given up their own persons to be experimented on by 

 themselves or others for the better settlement of some question 

 as to a process of disease ; have deliberately tried, for instance, 

 whether, in this way or in that, they could infect themselves 

 with the poison of plague or of cholera ; and as regards one such 

 case which is in my mind, I think it not unlikely that the illus- 

 trious life of John Hunter was shortened by the experimenls 

 which he did on himself with the ignoble poison of syphilis. 

 There have been cases, too, where criminals have been allowed 

 to purchase exemption from capital or other punishment at the 

 cost of allowing some painful or dangerous experiment to be 

 performed ou themselves. And cases are not absolutely un- 

 known where unconsenting human beings have been subjected 

 to that sort of experiment. But waiving such exceptions, the 

 rule is, as I have said, that scientific experiments relating to 

 causes of disease are performed on some animal which common 

 opinion estimates as of lo%ver importance than man. Now, as 

 between man and brute, I would not wish to draw any distinclion 

 which persons outside this room might find invidious ; Ijut, 

 assuming for the moment that man and brute are of exactly equal 

 value, I would submit that, -whew the life of either man or brute 

 is ^ to be made merely instrumental to the establishment of a 

 scientific truth, the use of the life should be economical. Let 

 me, in that point of view, invite you to compare, or rather to 

 contrast with one another, those two sorts of experiment from 

 which we have to get our knowledge of the causes of di-ease. 

 The commercial experiments which illustrated the dangerousness 

 of sewage-polluted water-supplies cost many thousands of human 

 lives ; the scientific experiments which with infinitely more 

 exactitude justified a presumption of dangerousness, cost the 

 lives of a few dozen mice. So, again, with experiments as to 

 the causation of tubercle :— judging from the information which 

 I quoted to you, I should suppose that the human beings whose 

 milk-supply on any given day includes milk from tubercular cows 

 might be counted, in this country, in tens of thousands ; but the 

 scientific experiments which justify us in declaring such milk- 

 supply to be highly dangerous to those who receive it were con- 

 clusive when they amounted to half-a-dozen. So far, then, as 

 regards the mere getting of experimental knowledge, we must 

 not, with a view- to economy of life, be referred to popular, 

 rather than scientific, experiment. And in the same point of 



view, it perhaps also deserves consideration that the popular 

 experiments, though done on so large a scale, very often have 

 in them sources of ambiguity which lessen their usefulness for 

 teaching. 



Let me now briefly refer to the fact that, during the last 

 quarter of a century, all practical medicine (curative as well as 

 preventive) has been undergoing a process of transfiguration 

 under the influence of laboratory experiments on living things. 

 The progress which has been made from conditions of vagueness 

 to conditions of exactitude has, in many respects, been greater 

 in these twenty-five years than in the t«enty-five centuries which 

 preceded them ; and with this increase of insight, due almost 

 entirely to scientific experiment, the practical resources of our 

 art, for present and future good to the world, have had, or will 

 have, commensurate increase. Especially in those parts of 

 pathology which make the foundation of preventive medicine, 

 scientific experiment in these years has been opening larger and 

 larger vistas of hope ; and more and more clearly, as year suc- 

 ceeds year, we see that the time in which we are is fuller of 

 practical promise than any of the ages which have preceded it. 

 Of course, I cannot illustrate this at length, but some little 

 attempt at illustration I would fain make. 



First, let us glance at our map. When we generalise very 

 broadly the various causes of death (so far as hitherto intelligibte 

 to us) we see them as under t\vo great heads, respectively auto- 

 pathic and exopathic. On the one hand, there is the original 

 and inherited condition under which to every man born there is 

 normally assigned eventual old age and death, so that, sooner or 

 later, he " runs down " like the wound-up watch with its ended 

 chain ; and, as morbidities under this type, there are those 

 various original peculiarities of constitution which make certain 

 individual tenures of life shorter than the average, and kill by 

 way of premature old age of the entire body, or (more generally) 

 by quasi-senile failure of particular organs. On the other hand, 

 as a second great mass of death-causing influence, we see the 

 various interfeiences which come from outside ; acts of mechani- 

 cal violence, for instance, and all the many varieties of external 

 morbific influence -vN-hich can prevent the individual life from 

 completing its normal course. 



As regards cases of the first class— cases where the original 

 conditions of life and development are such as to involve prema- 

 ture death (which in any such case will commonly show itself as 

 a fault in particular lines of hereditary succession) — the problem 

 for preventive medicine to solve is, by what cross-breeding or 

 other treatment we may convert a short-lived and morbid into a 

 long-lived and healthy stock ; and thi=, at least as regards the 

 human race, has, I regret to say, hardly yet become a practical 

 question. But, as regards cases of the second class, evidently 

 the various extrinsic interferences which shorten life have to be 

 avoided or resisted, each according to its kind ; and here it is 

 that the scientific experimenters of late years have been giving 

 us almost daily increments of knowledge. 



Two early instances, vastly important in themselves, though 

 of a comparatively crude kind, I have already mentioned ; and I 

 now wish to glance at some illustrations of the immense scope 

 and the marvellous exactitude of the newer work. 



The invaluable .studies of M. Pasteur, beginning in the facts 

 of fermentation and putrefaction, and thence extending to the 

 facts of infectious disease in the animal body, where M. Chau- 

 veau's demonstration of the particulate nature of certain contagia 

 came to assist them — they, I say, partly in themselves, and partly 

 in respect of kindred labours which they have excited others to 

 undertake, have introduced us to a new world of strange know- 

 ledge. We have learnt, as regards those diseases of the anirrial 

 body which are due to various kinds of external cause, that pro- 

 bably all the most largely fatal of them (impossible yet to say 

 how many) represent but one single kind of cause, and respect- 

 ively depend on invasions of the animal body by some rapidly 

 self-multiplying form of alien life. This doctrine, which scien- 

 tific experiment initiated, has, for the last dozen yeais, been 

 extending and confirming itself by further experiment. As soon 

 as the doctrine began to seem probable, science saw that, should 

 it prove true, it nmst have the most important corollaries. If 

 the cause of an infecting human disease is a self- multiplying gei-m 

 from the outside world, the habits of that living enemy of ours 

 can be studied in its outside relations. It becomes an object of 

 common natural history, it has biological affinities and analogies. 

 We can cultivate it in test-tubes in om- laboratories, as the 

 gardener would cultivate a rose or an apple, and we can see 



