In 1957, a doctor inSingaporenoticed that hospitals were treating an unusual number of influenza-like cases. Influenza is sometimes called “flu” or a “bad cold”. He took samples from the throats of patients and in his hospital he was able to find the virus of this influenza.There are three main types of the influenza virus(病毒). The most important of these are type A and B, each of them having several subgroups(亚群). With the instruments at the hospital the doctor recognized that the outbreak was due to a virus in group A but he did not know the subgroup. Then he reported the outbreak to the World Health Organization in Geneva. W.H.O. published the important news alongside reports of a similar outbreak in Hong Kong of China, where about 15-20% of the population had become ill.As soon as the London doctors received the package of throat samples, doctors began the standard tests. They found that by reproducing itself with very high speed, the virus had grown more than a million times within two days. Continuing their careful tests, the doctors checked the effect of drugs against all the known subgroups of virus type A. None of them gave any protection. This, then, was something new, a new influenza virus, against which the people of the world had no help whatever.Having found the virus they were working with, the two doctors now dropped it into the noses of some specially selected animals, which get influenza as much as human beings do. In a short time the usual signs of the disease appeared. These experiments proved that the new virus was easy to catch, but that it was not a killer. Scientists, like the general public, call it simply Asian flu.The first discovery of the virus, however, was made in mainlandChinabefore the disease had appeared in other countries. Various reports showed that the influenza outbreak started in mainlandChina, probably in February of 1957. By the middle of March it had spread all over the mainland. The virus was found by Chinese doctors early in March. But at that timeChinawas not a member of the World Health Organization and therefore did not report outbreaks of disease to it. Not until two months later, when travelers carried the virus into Hong Kong,China, from where it spread toSingapore, did the news of the outbreak reach the rest of the world. By this time it was well started on its way around the world. Thereafter, W.H.O.’s Weekly Reports described the steady spread of this great virus outbreak, which within four months swept through every continent. Why did the two doctors drop the flu into the noses of animals?