Virology and vaccines
Later on, the English bacteriologist F. W. Twort discovered a group of viruses called bacteriophages that infect bacteria and another scientist Felix d’Herelle described in his experiment that viruses when added to bacteria on agar can produce areas of killed bacteria. Moreover, he also accurately diluted a suspension of these viruses and discovered that the highest dilutions of virus can kill almost all the bacteria. By the end of the nineteenth century, viruses were considered an infectious organism. It has been shown that viruses can be grown only in plants and animals. However, in 1906, Ross Granville Harrison developed a method for growing tissue in lymph, and in 1913, scientists, namely, Steinhardt, Israeli, and Lambert, used this method to grow the vaccine virus in guinea pig corneal tissue. Moreover, in 1928, scientists Maitland and Maitland grew the vaccine virus in suspensions of hen’s kidneys. Furthermore, another breakthrough came in 1931 when the American pathologist E. W. Good grew inuenza and several other viruses in fertilized chicken’s eggs. Later on, in 1949, Enders, Weller, and Robbins grew the polio virus in cultured human embryonic cells. This was the rst method to grow viruses without using solid animal tissue, which enabled Jonas Salk to make an effective polio vaccine.