PHYSIOLOGY OF NUTRITION. 



the second heating, by which those which have germinated are 

 then killed. 



When our flasks, filled with sterilised food solution, and plugged 

 with cotton wool, are left to themselves, the fluid remains clear; 

 even after months it still remains so, since no development of 

 bacteria can take place. 



Pure cultures of Bacterium Termo, an organism very commonly 

 associated with putrefaction, can be comparatively easily obtained. 

 We prepare some Cohn's normal solution. This contains in 200 

 parts of water 1 gr. of acid Potassium phosphate, 1 gr. of Mag- 

 nesium sulphate, 2 gr. of neutral Ammonium tartrate, and O'l gr. 

 of Calcium chloride. In this case simple boiling of the solution in 

 the Erlenmeyer's flasks, closed with plugs of cotton wool, serves to 

 ensure sterilisation. We now pour water over some peas and let 

 them putrefy, transfer a drop of the bacterium-containing fluid to 

 the food solution by means of a glass rod, and if Bacterium Termo 

 develops, convey a drop of the solution to a fresh portion of the 

 nutrient solution. We repeat this process several times, till finally 

 a pure culture is obtained. In conveying the bacteria from one 

 portion of nutrient solution to another, we make use of a glass 

 rod sterilised by heating in a spirit flame. We lay it to cool on a 

 sterilised plate of glass under a bell-glass. It is a characteristic of 

 Bacterium Termo that the fluids in which it develops become 

 milky in the first days, and later acquire a greenish skin. Bac- 

 terium Termo exists in the form of rodlets, which are mostly 

 associated in pairs. These cells move to and fro by jerks. In the 

 zoogloea, which takes the form of the above-mentioned greenish 

 skin, are present immotile individuals. 



If some malt extract (prepared by treating malt powder with 

 water and filtering off the solution) is left to itself, the solution, 

 originally clear, becomes turbid in the course of a few days. By 

 microscopic examination it can be determined, in the manner to be 

 given below, that innumerable bacteria are present in the fluid. 

 At lower temperatures (about 15 C.) Bacterium aceti chiefly 

 shows itself, but at higher temperatures (about 50 C.), to which 

 we can readily expose the fluid in the thermostat, Bacterium acidi 

 lactici is found. According to Delbriick, 1 we can obtain the Lactic 

 acid fungus with certainty by treating 200 gr. of dry malt with 

 1000 gr. of water, and allowing the mixture, without filtration, to 

 remain for some time in a thermostat at 50 C. 



The hay fungus, Bacillus subtilis, is widely distributed in 



