f)94 DR A. LOCKHART GILLESPIE ON 



than the mean, while the rainfall was higher. The first two weeks of each attack, 

 taken collectively, were characterised by very different weather conditions. During 

 these 12 weeks, anticyclones prevailed in 9, cyclones in only 3, — exactly opposite to the 

 normal conditions in the mean of seven years. The temperature was again lower, while 

 the rainfall was less than half the mean, and about a third of the rainfall for the 

 preceding weeks. The distribution of barometric pressure for the 68 weeks of the 

 epidemics was normal, a remark which also applies to the mean temperature, while the 

 rainfall was slightly less. If the last two weeks of each of the epidemic periods be 

 considered separately from the total, we find that the type was normal, the rainfall 

 heavier, and the temperature a degree higher than the means for the same weeks in 

 seven years. 



I do not wish to draw any conclusions from these facts, but simply to state that the 

 figures adduced seem to suggest that a type of weather which is liable to cause catarrhs 

 and other affections of the respiratory tract precede the epidemics, but that the 

 occurrence of influenza in epidemic form does not appear to take place until another 

 and drier type has been established. In the preceding period evidences that the disease 

 is present are not wanting, but the number of cases are few. As the weather changes 

 the numbers go up with a rush. I had expected to find more evidence of excessive 

 rainfall at the close of the attacks than I did, for this was only marked in four out of 

 the six. 



A suggestion has been made that the cause of influenza might be disseminated, apart 

 from those cases carried by persons and by infected articles, by the currents of air, 

 especially by those induced by the state of barometric pressure termed anticyclonic. 

 The great majority of the pandemics of influenza have travelled over Europe from east 

 to west at that time of the year when the weather of the continent was dominated by 

 the great winter anticyclone which is almost constant at that period over Eussia and 

 Siberia. The air, following the well known rule that in anticyclonic systems the 

 currents flow out from the centre, is constantly flowing from east to west from Eussia 

 over the countries of Central Europe, and it has been supposed that the germs of the 

 disease might be disseminated by this current of air. It is quite possible that such 

 might occur. Several of the epidemics of these latter years, however, have not been 

 truly pandemic, and cannot thus be accounted for. On the other hand, as the move- 

 ment of the air in cyclones in this country is, regarding the cyclone as a whole, from 

 west to east, — the track of the majority of cyclones being in that direction, — one can 

 understand how an air-borne disease, postulating that influenza is air-borne, is 

 unlikely to be spread by the air-currents under such conditions. Apply this reasoning 

 to the facts noted above, and perhaps the supposed rapid spread of influenza on the 

 establishment of anticyclonic conditions may be explained. The air in the cyclonic 

 vortex, drawn chiefly from the atmosphere over the ocean, is moist, and contains none 

 of the contagion ; that of the anticyclone, derived from the higher strata, and thus from 

 distant cyclones, descending, blows gently over the land to the nearest cyclone, and, 



