56 HOUSE, GARDEN, AND FIELD 



step to the formation of vinegar led to search for yeast- 

 cells in the membrane of the vinegar- plant, and it was 

 discovered that they are regularly present. Since the 

 film which is now put into every domestic brew of vinegar 

 contains entangled in it a number of yeast-cells, we can 

 understand that it should make no difference whether a 

 teaspoonful of yeast is added or not. 



I have said that in former days housekeepers were not 

 particular to add a piece of vinegar-plant to every fresh 

 batch. Usually the vinegar formed all the same, and 

 when the process was at an end a membrane was found 

 covering the vinegar. They took very little notice of it, 

 and it is hardly mentioned in the old books. Perhaps 

 our forefathers regarded it as a disagreeable impurity ; 

 certainly they did not discover that this was the thing 

 that made vinegar for them. Where does the new vinegar- 

 plant come from, if no vinegar-cells have been put into 

 the solution ? 



The contamination, long unsuspected, of the vinegar- 

 bacteria with yeast- cells suggests the answer to the ques- 

 tion. When nutritive liquids are exposed to the air 

 without scrupulous precautions, a mixture of organisms of 

 different kinds and different powers is sure to result. The 

 old-fashioned housekeepers did not know exactly what 

 they were doing. Their yeast contained vinegar-bacteria ; 

 their vinegar-plants contained yeast-cells. All the vessels 

 which they used in making vinegar, in brewing, and in 

 bread-making, contained both of them, as also did the 

 dust and the very air of their houses. Now we see why 

 it made little difference whether they introduced a bit of 

 a film into their sugary mixture or not. They introduced 

 yeast, and their yeast contained vinegar-bacteria. All the 

 beer that they brewed no doubt contained vinegar-bacteria 

 too, but when the beer was tightly corked up in a cask 

 or bottle, carbonic acid being the only included gas, the 

 bacteria perished for lack of air ; had it not been for this, 

 all the beer would have turned sour. 



