1915] on Back to Lister 387 



Pasteur had isolated various yeasts or ferments, and bad shown that 

 some organisms were aerobic and some anaerobic, and that the words 

 vibrio and bacterium were beginning to be used. But as the time 

 went on two very important facts were made out. First, that only a 

 small proportion of the flora of the air are pathogenic ; and, secondly 

 (and this was one of Lister's own discoveries), that great dilution of 

 a septic fluid very much diminished its chance of infecting a putres- 

 cible medium. Thus typhoid pollution of the Nile in a few miles 

 ceases to be a source of danger, and one or two septic organisms 

 introduced into a vessel of blood serum will fail to grow. It is 

 really masses of particulate dirt which are dangerous, because they 

 contain colonies of organisms adequately protected from attack. 

 And, if this applies to attempts at infection of vessels containing 

 blood serum, still more does it apply to the dropping of isolated 

 staphylococci and streptococci on to a wound where the greedy 

 phagocytes are lying in wait to devour them. At every operation 

 scores of germs fall upon a wound — hundreds if it be prolonged — 

 but most of them are those of moulds and other innocuous vegetables 

 which have no chance of growing there ; and although there is a 

 possibility of an occasional pathogenic organism being among the 

 number, the risk of its developing is so small, that it is now generally 

 considered to be negligible, and that if one or two should escape 

 into the lymph channel, they will never elude the phagocytes in 

 spleen or bone marrow or elsewhere. 



I must now explain how the spray helped to prepare Lister for 

 the acceptance of Metchnikoff's discoveries. I said it was unpleasant 

 for all. There were some surgeons to whom it was positively 

 poisonous. Among these was a friend of Lister's, Thomas Keith, 

 the ovariotomist, whose field of operation was, of course, the peritoneal 

 cavity. In pre-antiseptic days he had obtained results that had 

 astonished the world, by dint of great dexterity, devoted personal 

 attention, and scrupulous regard to cleanliness. His success tried 

 the faith of some, but not of Lister, who was aware of the specially 

 high vitality of the peritoneum, and of other anatomical and physio- 

 logical peculiarities which diminish the chance of survival of germs, 

 but which are too technical for discussion here. 



Keith's success was so great thai he hesitated to adopt rigorous 

 antiseptic methods, and Lister at first dissuaded him from doing so, 

 fearing that carbolic acid might dangerously interfere with the 

 vitality of the peritoneum. Besides, at that time he did not fully 

 trust the efficacy of the spray. Keith did, however, for a time use 

 all Lister's methods, including the spray ; but this seriously interfered 

 with his health, so he abandoned it, and yet, when he gave it up, his 

 results continued to be as good as when he was using it. 



The germicidal powers of the peritoneum are great, but they are 

 only in degree greater than those of muscle fat and tissues. And 

 when it was found that other surgeons, some of them keen disciples, 



