VIRUSES 58 



familiar with the success which attended Pasteur's efforts to control rabies.. 

 This work was done even before viruses were recognized as distinct entities. 

 Pasteur passed the virus from the brain of a rabid dog to the brain of a rabbit, 

 and then passed it from generation to generation through rabbit brain. After a 

 long series of passages, he obtained an agent which produced only a very mild 

 disease in the dog but which, nevertheless, conferred immunity in the dog to 

 rabies. This same virus became the basis for the treatment of human beings sus- 

 pected of being infected with rabies . Distemper, another virus disease affecting 

 dogs and other household pets, has also yielded to the laboratory approach. Dis- 

 temper vaccine is now available and can be used to immunize young animals to 

 this disease. The control of foot and mouth disease of cattle is still somewhat 

 more crude, rhe English have maintained their country free of this disease by 

 very strict quarantine regulations and by a policy of slaughtering cattle which 

 shov; evidence of this disease. The British government pays out about a million 

 dollars annually to the farmers of Britain in payment for animals condemned and 

 slaughtered. There is very little evidence that the British public objects to 

 this expenditure. 



Probably many people are more interested in the control of human virus 

 diseases than in the control of diseases of plants and animals. The classic 

 story of virus disease control is that of smallpox. There was a time when small- 

 pox was one of the most hideous common diseases of the world, but today in more 

 civilized countries it is no longer a serious menace. This favorable change is 

 due in a large part to the development of vaccines. The development of smallpox 

 vaccine dates back more than a century before the recognition of viruses as sep- 

 arate or distinct entities. In the early part of the l8th century, a method of 

 control was introduced into England from the Hear East. It consisted of inocu- 

 lating a healthy human being with the exudate from a smallpox lesion. This 

 inoculation was done by scarifying the skin and simply applying the exudate. It 

 resulted in development of a few pustules. However, the disease v/as not nearly 

 as severe as smallpox, and it conferred an immunity toward smallpox, ihis con- 

 trol measure was dangerous because real smallpox virus was used in the inocu- 

 lation and the virus could spread to healthy individuals by the natural route 

 and cause disease. Nevertheless, it was a relatively effective procedure. It 

 was introduced in America in 1721 by Cotton Lather. It was still a subject of 

 bitter controversy at the time of the American Kevolution. During the latter 

 part of the l8th century, a young man in England by the name of Jenner observed 

 that the milkmaids who came into contact with cowpox lesions on the udders of 

 cattle seemed to be immune to smallpox. Jenner developed this observation and 

 introduced the practice of vaccinating human beings against smallpox with mater- 

 ial derived from the cowpox disease. The idea was received v/ith considerable 

 hostility in both iingland and America. Nevertheless, it did gain gradual ac- 

 ceptance. The American Indians were among the early ones to adopt Jenner's 

 vaccination, and they demonstrated their gratitude to the developer of the pro- 

 cess by sending him gifts. Napoleon vaccinated his entire amy against smallpox. 

 Per":aps one of the few accomplishments really to the credit of liapoleon was his 

 utilization of this advancement in science. Today vaccination against smallpox 

 is almost universally practiced in civilized countries. The vaccines now avail- 

 able may or may not have been derived from the cowpox originally used by Jenner. 

 There is some possibility that the present vaccinia virus, which is the material 

 used for smallpox vaccines, may have been derived from a mutation of smallpox 

 virus selected and developed by the cow. 



The conouest of smallpox did not have to await the advancement of knowledge 

 concerning the nature of viruses. However, most other virus diseases that have 

 been brought under control have been studied first in the laboratory. Yellow 

 fever affords a striking example. Many are familiar with the heroic story of 

 the field experiments of yellow fever carried out by the Army Yellow Kever Com- 

 mission. The name of Walter Keed is associated in many minds v;ith these experi- 

 TPents . Through them it was demonstrated that yellow fever is transmitted from 



