Vast Hordes Of Tiny Toilers Are Working In Our Service Night And Day To Keep The World Wholesome And All The Races Of Beings Supplied With Life-Stuff

T. M. Prudden.

We have learned that mould, yeast, and bacteria are microscopic plants (pp. 30, 128). Collectively they are called microorganisms (meaning little live things). How does yeast make bread light? How do bacteria make milk sour? Under what conditions does mould grow best?

Yeast causes fermentation. Some bacteria cause fermentation, but more cause that unpleasant kind of decomposition called putrefaction. Carbohydrate foods tend to ferment; protein foods tend to putrefy. In foods containing both carbohydrate and protein, whichever process starts first is likely to prevent or to check the other. The enzyms (p. 131) which exist in most foods also tend to decompose them.