NATURAL AND ACQUIRED IMMUNITY 113 



Hiul Guei'in) vaccine in their campaign against tuberculosis. Al- 

 tention is called in Chapter XXVII to the results of studies by 

 Park and his colleagues on immunization against tuberculosis with 

 B.C.G vaccine. They seemed to find the vaccine of little value in 

 human immunization. 



It is possible that a new acid-fast organism causing tuberculosis 

 in wild voles (small rodents) in England may be superioi' to B.C.G. 

 The organism originally isolated by Wells (1937) has been cultured 

 on Dorset's egg medium and employed by Wells and Brooks (1940) 

 to immunize guinea pigs against virulent human tubercle bacilli. 

 In their experiments they employed vaccines made from 2 strains 

 of vole acid-fast bacteria, to immunize two groups of guinea pigs; a 

 third group was immunized with B.C.G. vaccine while Group 4 con- 

 sisted of un vaccinated controls. Five months after vaccination. 

 Group 1 was injected with virulent human tubercle bacilli and 

 Group 2 with virulent bovine tubercle bacilli. Group 3 was divided 

 into 2 lots, one receiving virulent human and the second virulent 

 bovine tubercle bacilli. Similar treatment was given to Group 4. 

 The experiments were terminated after 11 weeks because of the 

 war. The results indicate that the vole vaccine gave almost com- 

 plete protection for Groups 1 and 2, that the pigs vaccinated with 

 B.C.G. all showed moderately progressive tuberculosis while the un- 

 vaccinated controls all showed extensive tuberculosis. 



It is interesting to note that the pigs vaccinated with the vole 

 vaccine did not react to 1 :1,000 dilution of O.T. while those vac- 

 cinated with B.C.G. were positive. The vaccinated animals, how- 

 ever, did react to lower dilutions of O.T. This work warrants 

 further investigation. 



Immunization With Killed Bacteria. — While it is generally 

 admitted that suspensions of living, attenuated organisms are 

 more potent immunizing agents than suspensions of killed bacteria, 

 the desire for safety has led to the widespread use of the latter. 

 If the organisms used in its preparation are obtained from the pa- 

 tient, the vaccine is described as an '' autogenous" one. When it is 

 prepared from a stock culture it is said to be a "stock vaccine." 

 If more than one kind of bacteria is included in the suspension, it 

 is called a "mixed vaccine." 



Since the term "vaccine" originally signified a preparation 

 of virus from vaccinia or cowpox, it is evident that its use to desig- 



