248 THE PRESERVATION OF FOOD PRODUCTS. 



killing bacteria spores has caused great losses of canned corn, peas, 

 and beans, as well as tomatoes. It must be recognized that, for 

 successful canning, every spore must be killed; for if a single one 

 be left alive in the middle of the can, the product is sure to spoil 

 (Fig. 50). The slowness with which heat will pass to the middle of 

 the can was not recognized until many losses had resulted from 

 insufficient heating. But the failures proved instructive, and after 

 bacteriologists studied the different problems presented by the 

 attempts to can food stuffs, the questions were answered one by 

 one, and successful rules were devised for the canning of any food 

 products subject to such methods. To-day failures are rare and 

 are all attributable to carelessness in the process. So thoroughly 

 has this subject been mastered that to-day any food that can stand 

 heat may be perfectly preserved by boiling and canning. Of course 

 the flavors are commonly changed by the process, and few of them 

 appear like the fresh material. But usually the flavors are less 

 changed than by any other method of preservation, and canned 

 goods are vastly superior to the dried foods with which our grand- 

 fathers were forced to be content in winter. Canning is especially 

 adapted to foods containing a good deal of water, and hence is 

 of especial use among foods that cannot be well preserved by drying. 

 Fruits are well adapted to canning, but ill adapted to drying, and 

 are ruined by salting. 



BACTERIA IN EGGS. 



The presence of bacteria in eggs results in trouble experienced 

 by every farmer, and one which it seems impossible to avoid. 

 It might be supposed that eggs, when freshly laid, would be free 

 from bacteria and hence not liable to decay. But this is certainly 

 not the case. Bacteria are known to enter the oviduct and contami- 

 nate the mass of the egg even before its shell is deposited. Hence 

 when the egg is laid it will commonly contain bacteria in greater or 

 less numbers. These bacteria can obtain plenty of oxygen from 

 the air that enters through the porous shell, and are thus able to 

 grow readily within the egg, where they soon cause its decay. A 



