YEAST 427 



It would be impossible for me to give the statement to you 

 with proper qualifications and limitations on an occasion 

 like this but there is also a sense in which it is true that 

 every animal body is made up of an aggregation of minute 

 particles of protoplasm, comparable each of them to the 

 individual separate yeast plant. And those who are 

 acquainted with the history of the wonderful revolution 

 which has been worked in our whole conception of these 

 matters in the last thirty years, will bear me out in saying 

 that the first germ of them, to a very great extent, was made 

 to grow and fructify by the study of the yeast plant, which 

 presents us with living matter in almost its simplest con- 

 dition. 



Then there is yet one last and most important bearing ot 

 this yeast question. There is one direction probably in 

 which the effects of the careful study of the nature of 

 fermentation will yield results more practically valuable to 

 mankind than any other. Let me recall to your minds the 

 fact which I stated at the beginning of this lecture. Suppose 

 that I had here a solution of pure sugar with a little mineral 

 matter in it ; and suppose it were possible for me to take 

 upon the point of a needle one single, solitary yeast cell, 

 measuring no more perhaps than the three-thousandth of 

 an inch in diameter not bigger than one of those little 

 coloured specks of matter in my own blood at this moment, 

 the weight of which it would be difficult to express in the 

 fraction of a grain and put it into this solution. From 

 that single one, if the solution were kept at a fair tempera- 

 ture in a warm summer's day, there would be generated, 

 in the course of a week, enough torulae to form a scum at 

 the top and to form lees at the bottom, and to change the 

 perfectly tasteless and entirely harmless fluid, syrup, into 

 a solution impregnated with the poisonous gas carbonic 

 acid, impregnated with the poisonous substance alcohol ; 

 and that, in virtue of the changes worked upon the sugar 

 by the vital activity of these infinitesimally small plants. 

 Now you see that this is a case of infection. And from the 

 time that the phenomenon of fermentation were first care- 

 fully studied, it has constantly been suggested to the minds of 

 thoughtful physicians that there was a something astound- 

 ingly similar between this phenomena of the propagation of 

 fermentation by infection and contagion, and the pheno- 

 mena of the propagation of diseases by infection and 

 contagion. Out of this suggestion has grown that remark- 



