Statistical studies in immunity : the theory of an epidemic / by John Brownlee.

  • John Brownlee
Date:
1907
Catalogue details

Licence: In copyright

Credit: Statistical studies in immunity : the theory of an epidemic / by John Brownlee. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

    6/42 page 486
    The result of these calculations has been to show that the curve of the solitary epidemic is singularly constant. It almost uniformly corresponds to that probability distribution which Professor Pearson has termed type IV., * so that this curve may be chosen for inter- polation, as one which gives a very clear representation of the facts. Even when the epidemic becomes symmetrical, it is to the form of type IV., where v is equal to zero, that the course approximates, and not to the normal probability curve. The precise limitation of an epidemic in point of time does not alter the form referred to, for in this case also the constants generally indicate a curve of type IV., though the latter is unlimited on either side. As the first example of curve fitting to the course of an epidemic wave, miliary fever (Table A, No. 1) f has been chosen. This instance does not afford an example of a curve which gives a good fit, but it is a disease of which the cause and the means of propagation are absolutely unknown, and therefore one which spreads as near as possible in natural conditions. It affects country districts, so that as new townships are invaded at all stages of the epidemic, and as these tend to become more numerous as the disease extends, a supply of susceptible persons is constantly furnished and a criterion given for the approximate estimation of the infectivity of the organism. It is, in addition, an explosive disease, and thus no difficulty arises about the start and close of the outburst. All the factors which make for the investigation of an epidemic type are thus present in this case. The course of an epidemic of this disease is illustrated in diagram I., along with the theoretical interpolation curve as well. As the number of persons exposed increased from the beginning to the end of the epidemic, it is seen that the decline in the number of cases must be due to the loss of infectivity in the germ itself, and not to the lack of individuals who may be supposed open to the contagion. Equally characteristic examples are afforded by the great plagues of London (Table A, Nos. 2 and 3). That of 1665 is specially interesting, as we have many contemporary accounts of the conditions which obtained. Great migrations from the city began as soon as the plague established itself, but the disease had barely begun to abate when the return * See Note at end of paper. t Rayer, Histoirc dr Vdpidimie de. Suettc Miliare en 1821, Paris, 1822.
    digitised image 1
    digitised image 2
    digitised image 3