Human Sperm Has a Surprising Tail Shape We've Never Noticed Before - 1

Surgical masks provide a measure of protection against a killer flu for American baseball players in 1918. That year—the final year of World War I—the Spanish flu took 50 million lives worldwide, at least three times as many as during the war.

Under siege by the Spanish flu epidemic of 1918, nurses in Lawrence, Massachusetts, treat patients in an outdoor hospital. Canvas tents kept the sick separated and less likely to spread the deadly virus. And with the success of fresh-air therapy on tuberculosis outbreaks, public health officials strongly recommended taking them outside.

Purplish samples of lung tissue from 1918 tell a story of disease and death. Scientists at the Armed Forces Institute of Pathology in Rockville, Maryland, hope to learn more about deadly flu viruses by reconstructing the gene sequence of the Spanish flu virus.

Spreading potentially lethal pathogens, influenza virus particles (brown) invade cilia (blue) in the airways of the human lung.

Armed with the tools for cultivating a flu vaccine, a scientist at the National Institute for Medical Research's World Influenza Center in London starts by drilling minute holes into fertilized chicken eggs. She will then inject the eggs with flu viruses that have most recently been circulating among the area population. After reaching a sufficient concentration, the samples will be tested to determine which strains of flu viruses are present. The strains that are most prevalent in the population will be used to develop flu vaccine for the following season.

A woman is mixing more than the ingredients for a meal in a pig-farming village near Nanchang in China's Jiangxi Province. Scientists believe the practice of living in close proximity to pigs and—in this woman's case—ducks plays a major role in contracting and spreading the H5N1 bird flu virus in parts of Asia. A flu virus that can attack a bird can rarely infect humans; the virus is unable to attach itself and grow in human cells. But a pig is capable of contracting the flu from birds as well as humans. When the two viruses mix within a pig, they can spawn a hybrid flu virus. If it begins to adapt and spread easily from human to human, the outcome can result in a deadly pandemic.

A wild duck takes to the skies over Alberta Province, Canada, after biologists tested it for avian flu. The flu virus originates in the guts of wild birds. Scientists are working to gain control of a new, deadly strain of bird flu—H5N1—that has mutated and is infecting humans.

Bundled up against the chill of autumn 2004, 69-year-old Ruby Vogelfanger waits in line outside New York City's District Health Center to receive a flu vaccine. A manufacturing problem with the vaccine produced by Chiron, one of only two suppliers for the United States, forced the company to withdraw its vaccines from the market, resulting in a severe shortage in the 2004-'05 season. On this October day, only a few hundred doses were available, designated for the city's older, "at risk" population.

Careful not to transport the H5N1 avian flu virus out of a contamination zone, veterinary workers disinfect their vehicle in the northwest region of Serbia and Montenegro. But car travel is just the beginning. If the virus begins to spread from human to human, jet travel will put the world at even greater risk.

Pigs sniff for food at a farm on the outskirts of Mexico City, where an outbreak of swine flu was blamed for the deaths of more than a hundred people in April 2009. Swine flu is a respiratory virus, spread from person to person. It originally jumped from pigs to humans in close contact with the animals, such as farmers.