156 GENERAL DISCUSSION 



shower passes through the body of an individual once a year. Another possibility 

 is that a small percentage of the primaries that come in would come down to 

 ground level and would produce highly ionizing secondaries. If highly ionizing 

 particles are more eflFective than x-rays, one could perhaps understand the lack of 

 results in x-irradiated animals. One would still expect to find an altitude effect; 

 for example, multiple sclerosis incidence in Denver should be higher than in New 

 York. Secondly, one would expect that in some way the incidence of multiple 

 sclerosis would correlate with the 11-year cycle. The primary cosmic radiation 

 events near the North Pole change radically in this 11 -year sunspot variation 

 period, and perhaps babies bom in periods of low sunspot activity might exhibit 

 a higher statistical incidence of multiple sclerosis. If heavy particles should cause 

 multiple sclerosis, this hypothesis could be tested by exposing embryos to radiations 

 produced in accelerators, such as the heavy alpha particles and other nuclei. 



John S. Barlow (Massachusetts General Hospital): The points made by Dr. 

 Tobias are well taken; I might make a few additional comments. Multiple sclerosis 

 per se is known only in man. There are naturally occurring demyelinating diseases 

 in animals, but as far as I know these exhibit no latitude effect. At a given latitude, 

 there are regional variations in the occurrence of the diseases, and it is an inter- 

 esting suggestion to determine whether these are correlated with variations in 

 background terrestrial radiation. The Auger showers may well be of biologic 

 importance, but I think that the energy of the original cosmic ray particles giving 

 rise to such showers is so great that no latitude variation for the showers would 

 be expected. Those few primaries that do reach the earth's surface certainly would 

 have a high relative biologic effectiveness, but they apparently are far over- 

 shadowed in numbers by similar secondary particles for which the latitude effect 

 is not very pronounced between 40° and 50° geomagnetic latitude and for which 

 an appreciable altitude effect is present. The question of variations with the 11-year 

 solar cycle merits further investigation. For several of the recent surveys of mul- 

 tiple sclerosis, data for a 10-year period were collected, and no systematic fluctua- 

 tion with time is apparent from these data. They have not, however, been exam- 

 ined, as far as I know, from the standpoint of year of birth of the patients, as 

 suggested by Dr. Tobias. Dr. John A. Simpson, of the University of Chicago, has 

 informed me that the solar variation at 50° geomagnetic north is about 25% and 

 decreases to some 6% at the geomagnetic equator; an effect of this size might 

 well be obscured in statistics for the disease collected for localities of latitudes of 

 50° or less. Studies in localities further north would be of particular interest from 

 the standpoint of the solar cycle. 



