224 BACTERIA, YEASTS, AND MOLDS 



or the cucumber until the flavors characteristic of sauerkraut 

 or dill pickles develop. 



There is a trick to making sauerkraut, and by no means 

 all the homemade or even the factory product is satisfac- 

 tory. Sometimes it putrefies instead of merely souring, and 

 the flavor becomes disagreeable. One important factor in 

 preventing putrefaction is the quantity of salt employed ; 

 one should use 2.5 per cent, that is, four tenths of an ounce 

 for each pound of cabbage. A second important factor is 

 the exclusion of air, as the desired bacteria grow in the 

 absence of air and the growth of other kinds must be 

 prevented. This can well be done by covering the jar with 

 a piece of cloth on top of which is placed a paraffined 

 board cut just to fit the jar. Weights are placed on this 

 to the extent of bringing the level of the juices up to the 

 board, but no higher. It should be watched carefully for 

 a few days, and weights removed or added so as to maintain 

 the proper level of the liquid. Using these simple precau- 

 tions any one should be able to make good sauerkraut. 



Bacterial Poisons in Foods 



But, on the other hand, there are unquestionably such 

 products which are harmful and which, even though 

 present in small quantity, may be decidedly harmful or 

 even poisonous. When certain kinds of microorganisms 

 grow in food material, they give rise to a class of decom- 

 position products which are sometimes, although from the 

 chemical standpoint incorrectly, called ptomaines. They 

 are usually the result of bacteria growing in animal prod- 

 ucts ; and while some of them are quite harmless, others 



