368 THE TREATMENT OF DISEASES. 



electrical or magnetic conditions of the atmosphere. A favourite theory years ago 

 was that it was caused by an excessive accumulation of electricity in the animal 

 economy. It occurs at all times of the year, and not especially at any particular 

 season. It is not dependent on cold or sudden variation in temperature, and it is 

 a mistake to suppose that such is the case. It is uninfluenced, too, by moisture, for 

 it is met with in the dry air of Upper Egypt, in the moist air of sea-coasts, and even 

 on the sea itself. 



It has been suggested that influenza might depend on the presence in the 

 atmosphere of an excessive quantity of ozone. Pure or atmospheric oxygen when 

 exposed to the action of electrical sparks is transformed into an odoriferous matter 

 called ozone, which is supposed to be merely a modified form of oxygen. Most 

 persons who have stood near an electrical battery at the time of its discharge must 

 have noticed a peculiar smell, and it is said the same odour pervades the air during 

 the prevalence of thunderstorms. It is asserted that the inhalation of strongly 

 ozonised air produces a painful affection of the chest a sort of asthma, accompanied 

 with violent cough, and from this it has been argued that ozone must be the cause 

 of influenza. The conclusion is certainly not justified by the premises, and the fact 

 that the disorder may prevail in a city or town, while a village a mile or two off 

 remains untouched, tells heavily against this theory. 



In some cases a thick and acrid fog has shortly preceded or has immediately 

 ushered in the influenza. We are told that the grippe of the spring of 1733 

 appeared in France immediately after offensive fogs, " more dense than the darkness 

 of Egypt." So also in 1775 it is recorded that the disease was ushered in by 

 " thick noisome fogs." In the same year it visited the shire of Galloway, in 

 Scotland, where " a continual dark fog and particularly smoky smell prevailed in the 

 atmosphere for five weeks, the sun being seldom seen." It is recorded, too, that in 

 1782 "the sun was for many weeks obscured by a dry fog, and appeared red, as 

 through a common mist." In 1837 " a dark fog brooded over the metropolis " during 

 the prevalence of the distemper. It has been observed, too, that during the 

 prevalence of these epidemic catarrhs various species of brutes and of birds have been 

 extensively affected with sickness, while on some occasions prodigious swarms of 

 insects have made their appearance. These statements are worth recording, but too 

 much importance must not be attached to them, for they may be mere coincidences. 



The main spread of influenza is not influenced by the wind, it does not move with 

 the same velocity, and it often moves against it. Yet it is probable that in some 

 cases the direction of the wind may have some share in its propagation. Thus we 

 are told that on April the 3rd, 1833, the Stag frigate was coming up the Channel, 

 and arrived at two o'clock off Berry Head, on the Devonshire coast, all on board 

 being at that time well. Half an hour afterwards, the breeze being easterly, and 

 blowing off the land, forty men were down with the influenza ; by six o'clock the 

 number was increased to sixty, and by two o'clock the next day to 160. On that 

 evening a regiment on duty at Portsmouth had a clean bill of health, but on the 

 following morning so many of the soldiers were affected by the influenza, that the 

 garrison duty could not be performed. 



It is no easy matter to decide whether influenza is infectious or not. The 



