ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 269 



tenuity of smoke particles, or of the minutest microbes, could be under- 

 taken, with a view to determine the rate and extent of its diffusion by 

 human communications, it would probably be found that very few dis- 

 tricts in the country are out of microbic touch, as it were, with all the 

 chief centers of population for a single day, and none for so long as a 

 week; and certainly the air inclosed in a packet from an infected place, 

 when suddenly liberated, would be likely to bear with it active seeds 

 of mischief. But the great majority of cases of influenza were due to 

 proximity to a person already attacked. Most people in the course of 

 a day come into association with ten or twenty others in more or less 

 confined spaces of air. If only one in five catches the influenza, and 

 so on in the same proportion, a fourth part of a large city may be struck 

 down in a very few weeks. In general, one-half or three-fourths escape, 

 being insusceptible, or less susceptible than others, or less exposed to 

 the virus. Where large numbers of persons work together in one ill- 

 ventilated building, the proportion of attacks is much higher, other 

 things being equal, thau where people work at their own homes. But 

 the frequent opportunities of infection at meetings, social gatherings, 

 public houses, in public conveyances, churches, and chapels tend to 

 reduce the inequalities which would otherwise be conspicuous. The 

 distance of air through which influenza can strike has not been well 

 ascertained, circumstances being very different, and some forms, such 

 as the catarrhal, being apparently more easily diffused than, others. 

 The maximum distance in the recent epidemics, for susceptible persons, 

 could hardly have been less than 100 feet in close air, and 4 feet in the 

 open. Isolation, where practiced, was successful in so far as it was 

 strict. But the intercourse of ordinary life makes isolation impossible 

 for the general population when once an epidemic of influenza has been 

 allowed to attack a number of centers. Strong measures against impor- 

 tation from other countries and immediate isolation and supervision 

 of the few cases which would occur might succeed in staving off a 

 national infliction, for the precautionary measures would not need 

 enforcement beyond the brief period of its j)revalence in neighboring 

 countries. Not only the high mortality, but the enfeeblement of millions 

 of breadwinners for months, years, and even for life has to be consid- 

 ered in connection with the expense of preventive measures. This 

 expense would only be a small fraction of the losses incurred by per- 

 mitting the pestilence to rage unchecked. 



As regards weather and climate, cold is distinctly conducive to the 

 spread of influenza, probably for several reasons : (1) The stillness which 

 often prevails in frost; (2) the closing of windows, etc., and the closer 

 association; (3) the greater prevalence of colds, bronchitis, etc., laying 

 open the breathing organs to attack. The first epidemic in London, at 

 the end of December, 1889, was ushered in by fog and frost, and appar- 

 ently rapidly reduced in severity by the mild and strong winds of the 

 latter half of January, 1890. The epidemics in succeeding years were 



