142 JOHN S. BARLOW 



primary protons in this category (Wilson and Wouthuysen, 1958), and the 

 latitude effect for such secondary protons is much less than that for primary 

 protons (their altitude effect is also appreciable). For these reasons, the 

 striking similarity between the two curves in Fig. 11 must be considered 

 fortuitous. 



Corrections to the Geomagnetic EflFect 



Since a rather narrow range of geomagnetic latitudes appears to corre- 

 spond to the zone of rapid increase in prevalence of multiple sclerosis, 

 further clarification of the details of the exact relationship between the lati- 

 tude effect for cosmic rays and the earth's magnetic field possibly may be of 

 importance for the present study (Katz et al., 1958). Thus, corrections for 

 local variations in the earth's magnetic field may be necessary to provide 

 a better fit for observed cosmic ray phenomena than geomagnetic latitude 

 per se. The dashed lines in Fig. 7 indicate isoprevalence lines constructed on 

 this basis and determined from data for cosmic rays published by Quenby 

 and Webber (1959). There is little difference in the location of the two sets 

 of isoprevalence lines in inhabited areas of the world except in central Asia, 

 and the circles in Fig. 5 indicate the corrections that would occur on this 

 basis for the two locations in this area represented in the figure. 



Discussion 



Cosmic radiation has been implicated as a factor in human disease in 

 other studies (Morris and Nickerson, 1948; Wesley, 1960), but the marked 

 latitude effect for multiple sclerosis appears to provide a greater possibility 

 for distinguishing between geographic and geomagnetic latitude as a param- 

 eter, a test which originally firmly established the relationship between 

 cosmic rays and the earth's magnetic field (Compton, 1933). 



The present data and that examined previously (Barlow, 1960) appear to 

 suggest that cosmic radiation in some way may be related to the occurrence 

 of multiple sclerosis. 



Since at a given location multiple sclerosis apparently is distributed ran- 

 domly among the susceptible population (Kurland et al., 1955) and since 

 plaques of demyelination of this disease are largely randomly distributed 

 in the white matter (Adams and Kubik, 1952; McAlpine et al., 1955), it 

 would be an attractive possibility to attempt to relate a randomly occurring 

 cosmic ray event to the trigger mechanism that Lumsden (1951) suggests 

 may occur in the initiation of plaques of demyelination. Several considera- 

 tions militate against such a direct relationship, if there is any relationship 

 at all between cosmic radiation and multiple sclerosis. Among these consid- 



