INTEODUCTION. XXXI 



diseases. The sourness, putridity, and other maladies 

 of beer Pasteur traced to special ' ferments of disease,' 

 of a totally different form, and therefore easily dis- 

 tinguished from the true torula or yeast-plant. Many 

 mysteries of our breweries were cleared up by this 

 inquiry. Without knowing the cause, the brewer 

 not unfrequently incurred heavy losses through the 

 use of bad yeast. Five minutes' examination with the 

 microscope would have revealed to him the cause of 

 the badness, and prevented him from using the yeast. 

 He would have seen the true torula overpowered by 

 foreign intruders. The microscope is, I believe, now 

 everywhere in use. At Burton-on-Trent its aid was 

 very soon invoked. At the conclusion of his studies 

 on beer M. Pasteur came to London, where I had the 

 pleasure of conversing with him. Crippled by paraly- 

 sis, bowed down by the sufferings of France, and 

 anxious about his family at a troubled and an un- 

 certain time, he appeared low in health and depressed 

 in spirits. His robust appearance when he visited 

 London, on the occasion of the Edinburgh Anniver- 

 sary, was in marked and pleasing contrast with my 

 memory of his aspect at the time to which I have 

 referred. 



While these researches were going on, the Germ 

 Theory of infectious disease was noised abroad. The 

 researches of Pasteur were frequently referred to as 



