单选题
An American survey has shown that each year every employed person loses three to four working days from colds and allied complaints, and every school child loses five to six days of schooling. Colds waste more time than strikes. The conquest of the common cold is therefore a thoroughly worthwhile ambition.
In 1961, Sir Christopher Andrewes found that the great killing infections like syphilis or poliomyelitis are each caused by one specific micro-organism, or, at worst, a small group of closely related parasites. By contrast it has slowly become apparent that the common cold is not a disease but a large group of similar diseases, caused possibly, by anything between fifty and one hundred different organisms.
Much of Sir Christopher"s book is taken up by an account of the struggle to identify, the genus which do cause colds. At first it was thought that bacteria were responsible because certain bacteria are commonly found in the noses and throats of cold victims. But Dr. W. Kruse of the Hygienic Institute of the University of Leipzig in 1914 provided the first evidence that a virus might be concerned by launching experimental infections.
Since that time thousands of volunteers have subjected themselves to similar experimental infectious, and for early twenty years most of such work has been done at Salisbury where the guinea pigs are rewarded by a ten-day holiday, all found that this "clumsy, expensive and unreliable" use of human volunteers was necessary because for a long time chimpanzees were the only other animals known to be susceptible to infection by common cold germs, and chimpanzees were far too expensive and unruly for routine use.
Growing cold viruses in the laboratory also proved difficult until one of the men involved demonstrated his possession of that most precious scientific faculty-serendipity.
Cold viruses were being grown with only moderate success in laboratory cultures of lung tissue from human embryos. The lung tissue cultures were kept alive by a salt solution containing added vitamins and a number of other ingredients. One day at Salisbury Dr. David Tyrrell found that this salt solution was faulty, and in order to keep his tissue cultures going he hastily borrowed a supply from another laboratory. When the imported solution was added to tissue cultures infected with cold viruses the lung tissue cells began to degenerate in a manner typical of tissues parasitized by active viral particles.
Dr. Tyrrell soon discovered that the borrowed fluid provided a more acid medium in his culture tubes than that produced by the native Salisbury brew. The nose provides a slightly acid environment, and Dr. Tyrrell realized that a degree of acidity was just what nose-inhabiting viruses needed in order to thrive outside the body. Thus a happy accident enabled a perspicacious scientist to modify the cold virus culture technique and thenceforward the whole exercise proved far easier and more profitable.
Much of common cold folklore is demolished. Draughts, chilling and wet feet do not bring colds on, says Sir Christopher, and clean, healthy living with lots of fresh air, plenty of exercise, good, plain food and a cold bath every morning may be good for the soul and the waistline, but does nothing to keep cold viruses at bay.
Colds are not very infectious — which will surprise most of us — so there is really no excuse for staying away from work when you have one. All the remedies so far invented have one thing in common — they are useless. In temperate countries, colds are commoner during the winter, but what the "winter factor" is which brings them on remains unknown. Most of us harbour cold viruses in our noses throughout the year, and many colds are probably not "caught" at all, but start because somehow the resident viruses become activated from time to time.
To write a book about colds at this stage, says Sir Christopher, is rather like writing a review of a play in the middle of the first act. Since he wrote those words, workers at Salisbury have announced the production of the first cold vaccine which will protect against infection by one particular cold virus. Unfortunately there are very many cold viruses and complete immunity from colds by vaccination would require the administration of a separate vaccine for every virus in the book.
单选题
The main reason why the common cold is difficult to deal with is that it