146 THE ACTION OF THE LIVING CELL 



observed instances of natural resistance, we must seek 

 further than the antibodies of classical immunology. 

 It is hoped that the reader will not misunderstand the 

 above statement. We do not wish to deride the results 

 of the brilliant investigators who have contributed so 

 much to the conquest of disease and the advancement 

 of our knowledge concerning the manner in which 

 higher animals protect themselves against their inva- 

 sion by more lowly forms of life. It is our desire rather 

 to stress the fact that while the formation of specific 

 antibodies towards invading organisms affords an ani- 

 mal some measure of protection against infection, 

 other physiological factors are perhaps of equal im- 

 portance in this respect. 



As is well known, many animals are resistant to- 

 wards diseases which ordinarily affect man; and con- 

 versely, man appears to be immune to some diseases of 

 animals, although careful study has failed to disclose 

 the existence of specific antibodies in the immune in- 

 dividuals. In consequence, the conclusion is forced 

 that factors other than specific antibodies must be in- 

 voked to explain such differences in susceptibility. 

 Judging from the remarks of such prominent inves- 

 tigators as Manwaring (1929) and Zinsser (1928), 

 the immunologists themselves have recently staged an 

 aboutface in the interpretation of such confusing 

 facts. 



According to the tenets of classical immunology, 

 only specific antibodies should be capable of combat- 

 ing the invasion of higher animals by bacteria or 

 other toxins. In recent years, however, there has been 

 accumulated a considerable volume of evidence which 

 shows that some infections may be overcome, at least 



