548 IMMUNITY 



destructive to them. The first experiments* of this kind on 

 animals appear to be those of Pasteur, who found that inocu- 

 lating animals with attenuated virus would immunize them 

 against inoculation with a strong virus or naturally acquired 

 infection. He promptl}^ succeeded with swine erysipelas, 

 chicken cholera, and anthrax. Later he succeeded with 

 rabies. Arloing, Cornevin and Thomas, and Kitt introduced 

 a successful method of preventive inoculation with attenuated 

 virus against blackleg. The method has been tried with a 

 number of other diseases with less satisfactory results. 



The next procedure w^as a line of investigations directed 

 toward the production of immunity by the use of toxins or 

 heated cultures of the bacteria. The first of these was an 

 immunization of pigeons against hog cholera by the use of 

 heated bouillon cultures of the bacillus of hog cholera by 

 Salmon and Smith in 1886. This method was followed with 

 similar results by Pasteur with chicken cholera. This line of 

 investigation led eventually to the immunizing of animals 

 experimentally with the toxins or heated cultures of certain' 

 virulent pathogenic bacteria such as diphtheria and tetanus. 



Another method that has been extensively tried experi- 

 mentally with the bacterial diseases, but usual!}' without suc- 

 cess, is the use of non-lethal doses of virulent virus. With 

 certain of the protozoan diseases this method is more successful, 

 as shown by the excellent results that are being reported in 

 immunizing cattle against Texas fever. 



It has been found that the blood serum of animals that 

 are immune to certain bacterial diseases possesses antitoxic 

 properties by which it is able to impart immunity to healthy 



*This principle was exemplified centuries before in the far East 

 where inoculation with small pox virus (material from the pustules) 

 was practiced whenever small pox occurred naturally in a very mild 

 form. Lady Mary Wortly Montague is said to have introduced this 

 practice into Europe about 17 18. Later, 1796, Jenner, after thirty years 

 of labor, introduced the practice of inoculating human subjects with the 

 virus of cow pox. This is known to-day as vaccination and the vaccine 

 is prepared at the present time from calves. In 1839, Thiele showed 

 that the disease known as cow pox was small pox in cattle. 



