the croonian lectures

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Annotations.

THE CROONIAN LECTURES.

"Ne quid nimis."

IN the second Croonian lecture at the RoyalCollege of Physicians of London Colonel J. G.Adami dealt with the difficult subject of adaptationin bacteria, and the consequent evolution of disease.After indicating the absurdity of thinking thatthe infectious diseases now known to us haveafflicted man from his first appearance on the

planet, he pointed out that if bacteria have been

present from the beginning of the world, this wouldnot imply that the specific infections have beenin existence for the same period, for zymoticphenomena must run parallel with geological,which teach differently. The reason why wecannot recognise the descriptions of epidemicsgiven by classical authors is not necessarily thatthey were incapable of noting characteristicsymptoms; more probably they described condi-tions no longer existing. It is known that inmore recent times infections have come and gone.The tritest example is the sudor anglicus, or"

sweating sickness," but many diseases have madetheir appearance in comparatively recent times-e.g.,diphtheria, cholera, syphilis. Here Colonel Adamiwarned his audience that a second principle mayhave to be considered. Certain of these diseasesmay have been present for an indefinite periodendemic in a particular locality, and then with theopening up of trade routes have spread rapidly.Admitting this, the conclusions reached by a studyof the geographical distribution of animals and

plants must also be admitted-i.e., where a species(such as the rabbit or sparrow) when introducedinto another continent shows an immediate spread-the fact that it was not there befojre forms anindication that the spread had arisen at a periodsubsequent to the separation of one continent fromanother. Whichever side was taken in the syphiliscontroversy, said Colonel Adami, it had to be con-fessed that this disease was non-existent in earlyEgypt or in the Rome of the time of Galen.The Croonian lecturer’s picture of the evolution

of an infection is very interesting :-If every infection is due to the diffusion through the body

of the toxins of one or other particular species of micro-organism, it deserves note that pathogenic microbes do notform an order by themselves, but, on the contrary, are

singularly diverse in their affiliations. With scarce an

exception every genus of micro-organism has its representa-tives among the pathogenic microbes, or, conversely, everypathogenic microbe has closely related forms differing fromit in little beyond the fact that the one is virulent, growingin or upon the tissues, the other non-virulent. Next, theseclosely allied species are found suggestively either growingin the cavities and on the mucous surfaces of the body, or inthe water and foodstuffs taken up by the individual. Thisstate of afEairs in itself strongly indicates that at someperiod or other pathogenic microbes have originated fromthose saprophytic on the body surfaces or existing in thefoodstuffs. This natural deduction has been opposed notablyby the German school of bacteriologists, with the late RobertKoch at their head, who stood out for the fixity of bacterialspecies." In studying bacteria two apparently opposite and

contradictory facts are to be made out: on the onehand they are extraordinarily conservative, but

1 A summary of the first Croonian lecture was published inTHE LANCET of June 16th (p. 921).

on the other there are certain changes of environ-ment which lead to certain and definite modifica-tions in the properties of bacteria, the orders ofvariation being usually given as three-fluctuations,mutations, and impressed variations or modifica-tions. Colonel Adami brought evidence forwardto show that in the bacteria at least what are

usually considered as mutations, or chance varia-tions, are in truth impressed variations due tospecific alterations in environment. Whereasunder the ordinary conditions of experimentcertain members only of a bacterial colonytake on the property of fermenting a foreignor new foodstuff, this condition of experiment canbe so altered that all the members of the colonywith absolute precision can be made to acquire thisnew property. The experiment can be so arrangedas to demonstrate that here is no question ofchance variation, of the survival of those forms,and those forms alone, which have exhibited varia-tion in a favourable direction-no question, that is,of survival of the fittest-but that there is, withincertain limits, direct adaptation in the Spenceriansense, direct equilibration between the organismand its environment. Certain experiments recentlyconducted by Major F. B. Bowman, C.A.M.C., withthe typhoid bacillus, proving this point, were givenin detail, and similarly, as an example ofvariation by loss of factors, there is theclassical experiment, ever quoted, of Pasteurand his lieutenants, Roux and Chamberland,in which by exposing any culture of theanthrax bacillus over a given period to a giventemperature of growth with absolute precision thepower of the spore production is lost, and nowfor years-and thousands of bacterial generations-grown under ordinary conditions spore produc-tion does not manifest itself. Now if this betrue of other properties, it must be true regardingvirulence, and we have methods by which we canexalt or depress the virulence and pathogenic pro-perties of bacteria, while we can take harmless

non-pathogenic bacteria and with absolute pre-cision, and not by chance variations, convert theseinto highly pathogenic virulent forms. It is thisdirect adaptation, evidently, that explains theorigin of the infections.

INCIDENCE OF INFECTIOUS DISEASE IN 1916.

THE report of the Medical Officer of the LocalGovernment Board on the incidence of notifiableinfectious disease during the year 1916 has nowbeen published and contains, as always, muchinformation of vital interest as to public health.As in previous years, the rates of infectioussickness in each thousand of the several popula-tions are given in the local tables for 1916. Thereturns indicate that a considerable proportion ofthe cases were imported from abroad, having beennotified at the seaports, which are therefore espe-cially exposed to danger. In England and Wales only4 cases of typhus fever were reported last year, ascompared with 45 in the year preceding. Scarletfever was notified in 75.722 instances, or fewer

by 51,364 than in 1915; diphtheria in 51,707instances, or 1890 fewer than in the precedingyear; enteric fever in 5564 cases, as comparedwith 6364 in 1915 (in 17 instances paratyphoidwas specifically mentioned). 1996 cases of puer-peral fever were notified, against 2057 in 1915;18,520 cases of erysipelas, as compared with 23,382 ;1306 cases of cerebro-spinal fever, against 2566