272 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



from the constant presence, and, as it were, the vaccinating influence, 

 of the germs in bad air. From similar reasons horses, when brought 

 from the country to London stables, very frequently fall out of sorts to 

 the extent, it is said, of 95 per cent, and sheep, when placed among 

 imported apparently healthy sheep, often fall sick. Texas cattle fever 

 is caught from apparently healthy cattle. The first intercouse between 

 Europeans and natives is attended with the introduction of fever, 

 dysentery, or other diseases. 1 



SEASONAL AND GEOGRAPHICAL DISTRIBUTION OF INFECTIOUS 



DISEASES. 



Many of the spreading diseases are more or less wont to rise toward 

 a maximum and to fall toward a minimum at certain times of the year, 

 and these seasons are generally nearly the same in similar climates 

 in the same hemisphere, but there are many particular instances of 

 variation. 



Scarlet fever is a disease chiefly prevalent in the northwest of Europe, 

 moderately prevalent in llussia, North America, and parts of South 

 America, the coast of Asia Minor, Italy, Turkey, and Greece, and quite 

 uncommon in Asia and Africa. It is not frequent in Australia. Its 

 maximum in London occurs in October, its minimum in April. In New 

 York its maximum is in April, its minimum in September. In Eng- 

 land, generally autumn is the time of maximum prevalence. In the 

 whole of Europe and North America 29.5 per cent out of 435 epidemics 

 are recorded as having occurred in the autumn, and 21.8 per cent in the 

 spring, the period of minimum 5 the remaining 4S.7 per cent took place 

 in summer and winter. A dry air with little rain seems to increase the 

 prevalence of scarlet fever. 



Measles, in London, has two maxima, one in December and a lesser 

 one in June, and two minima, one in September and one in February. 

 Measles occurs nearly all over the world since the great extension of 

 commerce, and seems to be little affected by climate. Cold weather, 

 however, favors it, as might be expected, since it infects through the 

 air of close rooms. 



Influenza, typhus, relapsing fever, smallpox, whooping cough, croup, 

 pneumonia, not only prevail most in cold weather, but in cold countries, 

 where there is least outdoor life and least fresh air in rooms and most 

 crowding. Diphtheria increases with the cold weather of autumn, but 

 tends to decline in February, and is at a minimum during the hot 

 months. Cerebro-spinal fever, which is a good deal connected with 

 crowding in large numbers in institutions, etc., not only attacks most 

 in cold weather, but in cold or temperate countries. The relation 

 between the temperature and the disease seems to be indirect; and the 

 causation and dissemination of the malady are obscure. 



1 Williams, quoted by Darwin, "Naturalist's Voyage." 



