476 



NATURE 



[February 9, 191 1 



INVESTIGATIONS OF PLAGUE. 



THE terrible intensity of the outbreak of pneumonic 

 plague now raging in Manchuria, and the presence 

 of plague-infected animals within our own borders, 

 have called forth recently a number of communications 

 on plague in the daily press. A special correspondent in 

 The Times, in two well-informed articles (December 

 22, 1910, and February 6, 1911), summarises the situa- 

 tion, and gives an admirable sketch of the principal 

 facts concerning the modes of spread of plague. Dr. 

 L. W. Sambon has also contributed two letters on the 

 subject to our contemporary. He cites some inter- 

 esting historical references to the preventive methods 

 adopted during epidemics of plague, but it is a pity 

 that he has allowed himself to fall into error on some 

 essential points in the epidemiology of the disease. 

 He remarks, for example, that in his belief trans- 

 mission from man to man is probably more frequent 

 than from rat to man. If Dr. Sambon bases this 

 statement upon personal experience of epidemics of 

 bubonic plague, it must be said that his observations 

 are directly opposed to the experience of many com- 

 petent plague workers. Dr. Ashburton Thompson, an 

 accepted authority, has stated that in Sydney plague 

 owes nothing of its epidemic form to contagion from 

 the sick. The view that bubonic plague is not directly 

 infectious is held unanimously by authorities in India. 



The Advisory Committee, appointed by the Secre- 

 tary of State for India, the Royal Society, and 

 the Lister Institute, has recently issued a further 

 volume of Reports on Plague Investigations in India 

 {Journal of Hygiene, vol. x.. No. 3). The volume 

 contains a number of articles which cannot fail to 

 interest all those concerned with plague administra- 

 tion. Briefly stated, It may be said that these investi- 

 gations confirm and amplify the conclusions already 

 recorded. 



The first article deals with the experimental pro- 

 duction of plague epidemics among animals. In 

 earlier experiments guinea-pigs were used, and it was 

 conclusively shown that epidemics could not be pro- 

 duced amongst these animals except when rat-fleas 

 (.\. cheopis) were present in the godowns or small 

 huts in which the experiments were carried out. 

 Gotschlich criticised these experiments on the ground 

 that guinea-pigs, unlike rats, do not feed on the 

 carcases of their dead companions. He believes that 

 among rats, plague is chiefly spread by the healthy 

 animals feeding on the carcases of those infected with 

 plague. In order to test the validity of Grotschlich's 

 criticism, wild Bombay rats, previously freed as far as 

 possible from fleas, were used in the present series of 

 experiments. The results show clearly that epidemics 

 occur among these animals only in the presence of 

 fleas. The Commission found no reason for thinking 

 that alimentary infection played any part in the pro- 

 duction of these experimental epidemics. This conclu- 

 sion completely agrees with their observations on the 

 mode of infection in naturally infected rats. 



The discovery by the Commission, in the early years 

 of their work, of chronic plague in naturally infected 

 rats, at first sight appeared to offer a plausible ex- 

 planation for the persistence of infection amongst the 

 rat population during the ofT-season, and for the re- 

 crudescence of the infection when the conditions again 

 became favourable for the epidemic spread of infection 

 amongst rats and human beings. From the evidence 

 available, the Commission showed considerable hesi- 

 tation in ascribing to these chronic plague lesions 

 any important part in the continuance and revival of 

 the rat epizootic. It leaned rather to the view that 

 the quiescent season is bridged over by sporadic cases 

 of acute rat plague. A great deal of fresh light has 

 been thrown upon this qu^s^'on in the volume under 

 NO. 2154, VOL. 85] 



review. A much more extensive experience of chronic 

 plague in rats in Belgaum, Poona, and Bombay has 

 fully convinced the Commission that the pathological 

 appearances described as chronic plague are stages in 

 the process of recovery from the acute disease. For 

 this reason, and because the term has been associated 

 with theories regarding the reappearance of the rat 

 epizootic, they regard the name "resolving plague" 

 as more appropriate. It is evident that the epidemio- 

 logical importance of chronic rat plague is on this 

 view considerably limited, if not, indeed, abolished. 



An interesting contribution to the problem of the 

 spread of plague through districts with numerous 

 scattered villages, will be found in this, volume. The 

 collection and arrangement of the extensive data deal- 

 ing with the recent history of human plague in three 

 districts in the Punjaub and the United Provinces 

 were undertaken by Major Lamb, I. M.S., and a 

 statistical analysis of the results has been made by 

 Dr. Greenwood. While the conclusions drawn from 

 this survey are necessarily tentative, they are of value 

 in suggesting a rational basis for effective plague 

 administration in the thickly populated districts in 

 India. It would appear that reimportation of the 

 infective agent is more likely to be the cause of 

 outbreaks in the villages than recrudescence. 

 Again, a study of the distribution of infected villages 

 in maps showing the position of affairs month bv 

 month, suggests a dissemination of the infection from 

 various centres. The statistical evidence does not 

 point to the conclusion that the infection of a village 

 renders it more liable to be infected during the next 

 following epidemic. 



The Commission has recorded its observations of 

 plague during the years 1908-9 in Belgaum and Poona. 

 The special reason for selecting these towns was that, 

 although not far distant from Bombay, the seasonal 

 prevalence of the human epidemics is different. It 

 had been already shown that in Bombay the rat-flea 

 prevalence varied at different seasons of the year, and 

 that the season of maximum rat-flea prevalence coin- 

 cided with the height of the epizootic. The intimate 

 relation between rat-flea prevalence and the spread of 

 rat and human plague is well illustrated in the present 

 observations. Moreover, the interesting fact is elicited 

 that a close connection appears to exist between the 

 flea prevalence and the hygrometric condition of the 

 atmosphere. 



The results at Poona show that the adverse factors 

 which combine to bring an epidemic to an end are (i) 

 a decrease in the number of fleas, (2) a decrease in 

 the number of rats, and (3) an increase in the propor- 

 tion of immune to susceptible rats. 



Mr. Sydney Rowland gives an account of his work 

 upon plague vaccines. This contribution, which is of 

 too technical a character to admit of a summary of 

 its contents, describes the results of an inquiry into 

 the immunising constituents of the B. pestis.^ The 

 results obtained are interesting, and suggest impor- 

 tant improvements in the method of preparation of 

 plague vaccines. 



The volume concludes w-ith a brief statement of the 

 provisional conclusions reached by the Advisory Com- 

 mittee as the result of the investigations made under 

 their direction from 1905-9 into the mode of spread of 

 plague in India. The Committee concludes, that in 

 nature plague is spread among rats by the agency of 

 rat fleas, and that, in the great majority of cases 

 during an epidemic of plague, man contracts the 

 disease from plague-infected rats through the agency 

 of plague-infected rat fleas. 



A perusal of this volume of reports must impress 

 fhe reader with the enormous amount of work en- 

 tailed in order to collect the evidence leading to these 

 conclusions. In this countrj- it is still little under 



