Studies on immune responses in afferent and efferent lymph of lymph nodes draining the tissues have contributed to the concept that primary immune responses are generated in the lymph nodes with a delay before antigen-specific effector cells arrive at the affected tissue.
Lightning strikes the ground approximately 25 million times each year in the U.S. According to the NWS, the chance of an individual in the U.S. being killed or injured during a given year is one in 240,000. Assuming an average life-span of 80 years, a person's odds over their lifetime becomes one in 3000.
Where does on our planet does lightning flash most frequently? According to satellite observations, lightning occurs more often over land than over the oceans. And lightning seems to happen more often closer to the equator. The map above shows the average yearly counts of lightning flashes per square kilometer from 1995 to 2013. Areas with the fewest number of flashes each year are gray and purple; areas with the largest number of lightning flashesâas many as 150 per year per square kilometerâare bright pink.