INFECTION AND IMMUNITY. 433 



be accepted as conclusive, have, nevertheless, offered 

 a number of most significant suggestions, not only in 

 connection with several obscure features of this disease, 

 but also in relation to the establishment of tissue 

 resistance. 



They found but little difficulty in affording immunity 

 to animals that are otherwise susceptible to the patho- 

 genic action of the organisms concerned in the pro- 

 duction of this disease, 1 by the introduction into their 

 tissues of the products of growth of the organisms from 

 which the latter had been separated. The immunity 

 thus produced is seen in some cases to last as long as 

 six months ; again it is seen to disappear suddenly in a 

 way not to be explained. It was seen in one case to be 

 hereditary. 



The energy of the substance that has the power of 

 affording immunity was seen to be very much increased 

 by subjecting it to temperatures somewhat higher than 

 that at which it was produced by the bacteria. The 

 Klemperers found that if this substance was heated to a 

 temperature of from 41 to 42 C. for three or four days, 

 or to 60 C. for from one to two hours, intravenous 

 injection was followed by complete immunity in from 

 three to four days; whereas, if the unwarmed material 

 was used, immunity did not appear before fourteen days, 

 and then only after the employment of relatively large 

 amounts. Moreover, when the previously heated pro- 

 ducts are introduced into the circulation of the animal, 

 the systemic reaction is of but short duration, but if the 

 unwarmed substance is employed, immunity is manifest 



1 Animals do not, as a rule, present the pneumonic changes seen in human 

 beings. The introduction of the micrococcus lanceolatus into their tissues 

 results, in the case of susceptible animals, in the production of septicaemia. 



