120 JOURNAL OF THE [November, 



In this condition, the organism, though able to bear for a long 

 time the heat of boiling water, neither grows nor multiplies. 

 Nevertheless, upon the return of favorable conditions, the spore 

 expands and resumes its power to multiply. For destroying 

 bacteria the student pursues the following method : The so- 

 lution containing them is boiled ten minutes. This kills the 

 bacteria but not their spores. Next, the solution is put in a 

 warm place and left there for two or three days, during which 

 the spores develop into bacteria, and it is then subjected to 

 boiling heat again. This process is repeated until all the spores 

 have developed into bacteria and have in that form been de- 

 stroyed. Steam or dry heat is equally efificacious for this 

 purpose. 



Certain substances have been found which destroy bacteria 

 These we call disinfectants. Carbolic acid is one. In our lab- 

 oratory we use corrosive sublimate of the strength of one part 

 to a thousand. With this we wash our hands. It does not 

 hurt the hands, but effectually destroys the bacteria. In this 

 are washed also the implements used in experiments with 

 bacteria. 



Bacteria absorb their food through the cell-wall, and through 

 the same passes out the rejected material. They feed on all 

 animal and vegetable substances which decay, and from them 

 eliminate the original elements of which those substances 

 are composed. They separate the carbon, hydrogen, nitrogen 

 and sulphur from dead animal tissue, sending off therefrom as 

 carbonic acid and nitric acid the carbon and nitrogen. In the 

 absence of bacteria the earth would be cumbered with things 

 dead that once had lived. Bacteria, the yeast plant, mould 

 plants, etc., are necessary to our existence. They ripen our 

 cheeses, and through their agency the curd or cream of milk is 

 transformed into cheese. They bleach linen and cotton. They 

 combine the oxygen and nitrogen of the atmosphere. Without 

 them there would be no gunpowder nor nitro-glycerine. They 

 are supposed to have been largely instrumental in the produc- 

 tion of coal, and in changing coal into petroleum. They are, 

 perhaps, involved in the process of animal digestion. 



But bacteria do not always perform welcome offices. Occa- 

 sionally, products of certain of them bring disease and death to 

 man. Sausage and other m^ats, containing such products, have^ 



