193 PROFESSOR LISTER, 



is this. Having induced the lactic fermentation in a glass of 

 pure boiled milk by means of our presumably pure ferment, and 

 estimated the number of bacteria per minim, I diluted with boiled 

 water accordingly and then proceeded as follows : — These five 

 covered test-tubes which you see before you, containing boiled milk 

 in their lower part, were inoculated each with a drop calculated to 

 contain two bacteria; these other five similar test-tubes were inocu- 

 lated each with a drop calculated to contain one bacterium ; these 

 five liqueur glasses were also inoculated with drops each calculated 

 to contain one bacterium; and one other liqueur glass with a drop 

 calculated to contain four bacteria. The result was that the specimen 

 with the drop calculated to contain four bacteria soured and curdled 

 in a few days; and all these five calculated to have two bacteria to a 

 drop curdled also in a few days. The milk, you see, is perfectly 

 solid. You will also observe that no other change has taken place 

 except the lactic fermentation, no O'ldlum lacfis has grown, and 

 no other alteration has taken place ; it is as pure in whiteness as 

 when it was first coagulated. I may here mention that, although 

 all these coagulated, they did not all coagulate at the same time. 

 There was a time in the twenty- four hours during which the coagu- 

 lation went on, in which I hoped that some of them were going to 

 be permanently fluid, implying, as you would expect, that the 

 particles of the ferment were not uniformly distributed ; some had 

 more than others, though each happened to have at least one. But, 

 of the five test-tubes calculated to have only one bacterium on the 

 average to each inoculating drop, three have remained fluid, and 

 so have two of the liqueur glasses ; so that, of the ten calculated 

 to have on the average one bacterium each, exactly five, it so hap- 

 pens, have remained fluid without any curdling. I may consider 

 myself somewhat fortunate that I have succeeded in bringing 

 these specimens all the way from Edinburgh in this condition. I 

 will now deprive this one of the protection in which it has hitherto 

 lived. [Professor Lister, having removed the glass shade and 

 glass cap from one of the liqueur glasses, proceeded to 

 drink part of its contained milk.] It is perfectly sweet. It 

 has a slight flavour of suet, which M. Pasteur has described as 

 resulting from the oxidation of the oleaginous material of the milk. 

 If any gentleman likes to taste it after the lecture, he can do so. 

 Let me note this curious circumstance, that, of those specimens 

 which did coagulate, those in the tubes coagulated considerably 

 earlier than those in the more open vessels. At first, it seemed 

 as if, for some strange reason, those in the open vessels were 

 going to remain permanently fluid — even that which had, accord- 

 ing to the calculation, four bacteria to the drop. I presume this 

 is to be explained on the same principle as Pasteur has explained 

 a corresponding fact with regard to the yeast-plant. He has 



