GEOGRAPHIC DISTRIBUTION OF MULTIPLE SCLEROSIS 139 



disease, however, the latitude trend is considerably more poorly defined, 

 although there is some suggestion of an increasing mortality with increasing 

 latitude. Further, there is little to choose between the geographic and the 

 geomagnetic plots for Hodgkin's disease. 



Latitude Effect for Cosmic Rays 



The statistics for multiple sclerosis that have been examined here, as well 

 as those considered previously (Barlow, 1960), appear to suggest that the 

 geographic distribution of this disease is better correlated with geomagnetic 

 latitude than with geographic latitude. Since the phenomenon of cosmic 

 radiation is the only one known to be related to geomagnetic latitude,^ it is 

 appropriate to examine the latitude eflfect for various cosmic ray parameters 

 for comparison with the latitude effect for multiple sclerosis. Variation with 

 altitude must also be considered. For multiple sclerosis the available data 

 do not indicate any clear variation with altitude (Barlow, 1960), whereas 

 for cosmic rays the altitude effect is generally large compared to the latitude 

 effect. Such is the case for the ionization produced by cosmic rays as deter- 

 mined by an ionization chamber (Fig. 9). At sea level, the latitude effect 

 between 0° and 50° is only 14%, a much smaller effect than is apparent in 

 Figs. 2-6. Between 40° and 50°, it is even smaller. The altitude effect of 50°, 

 however, is such that there is about 70% more ionization at an altitude of 

 2,000 meters (6,500 feet) than at sea level. 



The latitude effect for multiple sclerosis thus is not in accord with that for 

 the ionization produced by cosmic rays, except some of the data for multiple 

 sclerosis are suggestive of a "knee" at about 50°, and a "knee" at this lati- 

 tude is apparent in Fig. 9. Neither the meson component nor the nucleonic 

 comp)onent (protons and neutrons) of cosmic rays near sea level had a 

 latitude effect as pronounced as multiple sclerosis apparently has. 



More pronounced latitude effects are found at the top of the atmosphere 

 (i.e. at about 80 kilometers or 50 miles), at heights where the atmosphere 

 has not yet exerted its filtering and diffusing effects on the incoming cosmic 

 ray flux. Thus, the total number of particles incident vertically at high lati- 

 tudes is some ten times greater than the number incident at the geomagnetic 

 equator (Fig. 10). Such a curve represents the flux for primary particles of 

 all energies, and if specific energy ranges are examined, even more pro- 

 nounced latitude effects are apparent, as indicated in the theoretically com- 

 puted curves reproduced in Fig. 11. The sigmoid curve from Figs. 2-6 has 

 been included in Fig. 11, and a close parallel is seen between this curve and 

 that for primary cosmic ray protons of 4.5 Bev energy. This order of energy 



" The aurora borealis and australis appear to be indirectly related to cosmic radiation 

 and the earth's magnetic field through the intermediary of the van Allen radiation 

 behs (van Alien, 1959). 



