June 1 6, 1 881 J 



NA TURE 



145 



Jan. Feb. March. April 



o.— Atrophy ;ind Debility. 



eight epidemics of whooping-cough 

 during the thirty years, with the in- 

 structive result that the curve for each 

 of the separate epidemics was sub- 

 stantially identical with the general 

 curve for the whole thirty years" period, 

 each of the four prominent phases of 

 e.ich curve occurring all within a week 

 of each other. As regards the small- 

 pox curve, if the deaths during the 

 epidemic of 1870-72, by far the most 

 fatal of all the epidemics during the 

 thirty years, be deducted from the 

 general result, we obtain a curve 

 which is substantially the same 

 curve as that for the whole thirty 

 years, but only less pronounced. From 

 ihcic results it follows, and the remark 

 is of general application to all the 

 curves, that the mortality curves for 

 the different diseases arrived at in 

 this inquiry may be regarded as true 

 constants of these diseases for London. 



The climate of London, looked at 



- as influencing the health of the people, 



may be divided into six types of 



weather according to the season of 



the year. These are respectively — 



Period i.— Damp and cold, fourth 

 week of October to third week of 

 December. 



Period 2. — Cold, fourth week of 

 December to third week of February. 



Period 2. — Dry and cold, fourth 

 week of February to second week of 

 April. 



Period 4. — Dry and warm, third 

 week of April to thirl week of June. 



Period 5. — Heat, fourth week of 

 June to first week of September. 



Period 6. — Damp and warm, second 

 week of September to third week of 

 October. 



The outstanding features of the 

 death-rate in its relation to the varying 

 types of weather through the year are 

 shown by the top curve of Fig. 4, 

 ^ which represents the total mortality 

 for all ages. This curve shows two 

 maxima in the course of the year : 

 the one, by far the larger of the two, 

 extending over six months from No- 

 vember to April, and the other em- 

 bracing the period from about the 

 beginning of July to the autumnal 

 equinox. It will be also obsei-ved that 

 the comparatively short-continued but 

 strongly-pronounced summer maxi- 

 mum is restricted to mere infants, 

 whereas the larger winter maximum 

 is a feature of the curves for all ages. 



Figs. 5 to 10 are representative 

 curves of those diseases which go to 

 form the summer maximum when 

 •■heat" is the chief characteristic of 

 ■.he weather. The direct relation of 

 ihe progress of mortality from diar- 

 rhoea to temperature is strikingly seen 

 in the startling suddenness with which 

 the curve shoots up during the hottest 

 months of the year, and the sudden- 

 ness, equally startling, with which it 

 falls on the approach of colder weather. 

 The cur\es for dysentery, British 



