1899] MICROSCOPICAL JOURNAL. 335 



they cause a shrinkage or expansion beyond recognition. 

 That the changed appearance noted in the tissue is due, in 

 part at least, to the altered condition of the water in the 

 tissues. The nitrate of silver, for example, has so changed 

 the water of combination that the bacteria cannot pene- 

 trate the film thus formed with the tissues, and the bac- 

 teria in the tissue have either had sufficient water re- 

 moved from them to cause their death, or else have be- 

 come so confined that they cannot get the water necessary 

 for their proper growth. The soil has in reality become 

 hardened, insomuch as it is now insoluble to their diges- 

 tive action, and might with truth be called antiseptic. 



In proof of the importance of rendering the water in 

 the tissues inaccessible to bacteria, and that the. way the 

 cells render themselves germicidal is by removing the 

 water from the bacteria themselves, or else so placing the 

 water of the tissues as to be insoluble to the digestive 

 action of bacteria, it is necessary to explain why foods are 

 preserved from the action of bacteria by cooking, dry- 

 ing, freezing, salting, sugaring in alcohol, acids, alkalies 

 and oils. 



In cooking foods, boiling, frying, baking, etc., the wa- 

 ter is driven out of them, so that they shrink quite be- 

 yond recognition. Bacteria, when present, of course, 

 are generally killed, and those that may get lodgment do 

 not grow well, owing to the decreased quantity of water 

 now present in the tissues. Freezing solidifies*the water 

 in the tissues, and while they remain frozen the water is 

 inaccessible to bacterial growth. Drying removes t}»e 

 water of combination in part, so although the tissues may 

 be covered with bacteria, the bacteria do not grow ; not 

 because the bacteria are dead, but because they cannot 

 get the water necessary for their growth. Tiie proof that 

 it is only water that is needed, anyone knows who has had 

 experience with dried foods that have become damp. In 

 the use of smoke as applied in curing hams, bacon, etc.. 



