294 HEALTH AND DISEASE 



c) Compare putrefaction with fermentation as to odor and 

 general characteristics. It will be found that carbohydrates 

 ferment through action of yeasts and that proteids putrefy 

 through activity of bacteria. 



5) Hay bacillus: 



a) Cut hay into short pieces and pour boiling water upon it. 

 Cover and set aside for several days. Observe carefully from 

 day to day cloudiness and formation of scum, indicating multi- 

 plication of bacteria. 



b) When scum is developed, examine under microscope and 

 note many rod-like bacteria (hay bacilli). 



6) Molds: 



a) Moisten pieces of bread and of cheese, put on plates and 

 cover tightly with tumblers. Leave for several days, observing 

 growth at intervals. 



b) When molds are well developed, examine under micro- 

 scope and note their characteristic forms. 



c) Take up some of mold on point of a needle and touch it to 

 several points on surface of a fresh piece of bread. Moisten 

 and set aside under tumbler, as before. Note whether mold 

 develops more quickly at points touched than elsewhere. 



7) Determination of number of microbes by culture: 



a) Melt 6 test tubes of gelatine by placing in water at a 

 temperature of about 120 F. When thoroughly melted, re- 

 move the cotton from test tube and, by means of a small glass 

 tube which has been sterilized by boiling or heating in a flame 

 and then cooled, introduce 1 cu. cm. of well or tap water. Re- 

 place cotton and mix water thoroughly by shaking but do not 

 get it upon cotton. Remove cotton and pour into sterilized Petri 

 dish. Cover dish immediately and allow to stand at room 

 temperature for from 24 to 48 hrs. Observe contents of dish 

 from time to time without uncovering it. 



b) When small white dots representing colonies of microbes, 

 each of which has grown from a single microbe, are distinctly 

 visible, count them and thus determine number of microbes in 

 cu. cm. of water used. 



used, such as methylene blue and methyl green. The blue or 

 green is dissolved in a drop of water, which is then allowed to 

 flow under the cover glass into the sediment. A small piece of 

 blotting paper placed upon the opposite side of the cover glass will 

 assist the flow. 



