1891.] MICKOSCOFICAL JOURNAL. 177 



pounds, like water, carbonic anhydride, and ammonia, and elaborate 

 them into complex compounds suitable for the food of animals. Ani- 

 mals, on the other hand, break down these complex substances and 

 furnish them again in the simplest forms available for plant food ; but 

 still there is a large number of animal products that are not thus re- 

 duced, and not suitable for plants to assimilate. " These it is the func- 

 tion of the bacteria to transform and prepare. They are the cooks of 

 the vegetable creation. Every fermenting manure heap, every rotten 

 vegetable and animal is a great kitchen in which this preparation of 

 vegetable, food is going on. But for the constant beneficent work of 

 the bacteria the world would soon be choked up with the undecompos- 

 ing remains of plants and animals ; and vegetable and animal life must 

 alike perish. They are at once, then, the scavengers, caterers, and 

 cooks of nature, and as no living beings are so widely distributed, so 

 no living beings are more beneficent in their work."* 



In an interesting investigation at the city of Paris, it was found that 

 in a cubic metre of air above ground there were ten thousand germs ; 

 in the sewers, thirty-six thousand ; in old houses, forty thousand, and 

 in the hospital of Petie, seventy thousand. Dr. Percy F. Frankland has 

 also shown that the number of bacteria present in the air differs at dif- 

 ferent seasons of the year, the largest number being found during the 

 summer months. 



These micro-organisms are absorbed by water exposed to the air, find 

 Dr. Frankland has found that the average river water of England, like 

 that of the Thames, contains about twenty thousand germs per cubic 

 centimetre. This number is greatly reduced when the water is sub- 

 mitted to storage and filtration, for the purified water from the Thames, 

 used in London, contains only about four hundred germs per cubic 

 centimetre ; but thei"e is, perhaps, no reliable artificial method for their 

 entire removal, except by the agency of heat, and by slow filtration 

 through compact substances. 



The bacterium termo, which is the agent of putrefactive decomposi- 

 tion, is found abundantly in polluted water. If a bottle of such water 

 be left in a warm place for a few days, the water acquires a disagree- 

 able odor, and upon microscopical examination is found teeming with 

 these micro-organisms and other low forms of life. Or, if a glass of 

 the water is left uncovered for a few days, a thin coating will form on 

 its surface, which, if placed under a microscope with a magnifying 

 power of about five hundred diameters, will present an interesting field. 

 In the words of Troussai't, " The whole field of the microscope is in 

 motion ; hundreds of bacteria, resembling minute transparent worms, 

 are swimming in every direction, with an undulatory motion like that 

 of an eel or snake. Some are detached, others united in pairs, others 

 in chains or chaplets, or cylindrical rods." These bacteria multiply 

 and develop in endless succession, in accordance with the laws ^f their 

 being, and they are significant of organic pollution. They purify water, 

 however, by converting the organic into inorganic, and therefore harm- 

 less constituents. But a water which contains them in any great num- 

 bers should always be considered with suspicion. 



In some instances bacteria are capable of being conveyed to great 

 distances in w^ater without losing the vitality necessary to produce fer- 



* The Sanitary Era, March, i8go. 



