and Laboratory Methods. 1107 



questions stated in tlie Laboratory M;inual. On<; of tin: |)ap(;rs prepared rlurini^ 

 a recitation period is reproduced in J'ig. 2. I'i^iircs .'5 and 4 arc drawin^yi ol 

 l^etri dish cultures made by two other pupils. 



One of the boys, not satisfied with the anrifjunt <<f lai^fjratory work ^ivcn in 

 school, prepared nutrient gelatin at home. He writes thus of his experiences: 



" I took about a half pound of lean beef and after cutting into pieces placed 

 in a [jot and covered with water, then brought to a boil. I should also mention 

 that I used a moderate fire so that the process occupied about twet)ty minutes. 

 After obtaining my broth I added gelatin and brought again tf; a boil. Here I 

 added some salt and carbonate of soda, after which I strainerl the broth through 

 cotton into a sterilized bottle and corked. 



" I experienced such trouble in clearing the gelatin of colonies that I hnally 

 melted the gelatin and poured it into test tubes and in them brougfit if to a boil 

 with the result of one tube burnt and five cleared. In three of the tubes Mr. I'ea- 

 body inoculated pure cultures; one of the tubes has proflueed a very large red 

 colony, the others have not grown." 



This laboratory work on the growth of bacteria was followed by an «;xperi- 

 ment performed at home by the pupils. On(; of tlu; girls gives the following 

 report of her work : 



"Tjik Hiiiiiv Ol iiACTKkiA IN Mn.K. I procured three bottles of about th*; 

 .same size. 1 then thoroughly cleansed each bottle before I used it. 'I'wo ol 

 the bottles had stoppers ; the other had none. One of the bottlf;s I lialf filled 

 with good fresh milk, put the sto|;per on, and set it outside the window. I 

 labeled this bottle 'No. 1.' 



"Into the second bottle 1 poured about the same amount, oi rnilk, and set it 

 aside in a warm temperature of about 70'\ I labehrd it ' No. 2.' 



"The third bottle I cleaned in very hot water. I then boiled the same 

 amount of milk that 1 put in each of the other bottles. 1 allowed it to boil for 

 about three minutes. After the milk had cooled a little J poured it into the thirri 

 bottle. I placed it beside bottle No. 2, and labeled it 'Sterilized Milk.' 



" At the end of fifteen hours 1 examined each of the bottles. I noticed that 

 No. 1 had very little smell at all. No. 2 had a .sour like smell. It smelled as if 

 the milk were turning. No. 8 had hardly any smell at all, Jf there was any smell 

 at all, it was a sweet one. I now boiled the milk in \o. '•', again. 1 first 

 thoroughly cleansed the bottle and cork before I put the rnilk in. I then placed 

 it Vjeside No. 2, and put No. 1 again outside the window. 



"At the end of twenty-four hours I again examined my bottles. I found 

 that No. 1 had not any smell at all. .No. 2 had a very decidedly .sour smell, and 

 No, 8 had a sweet smell. 



" The changes in the milk are due to the growth of the bacteria from the air, 

 or on the bottles, or the stoppers. As far as my experiment has worked I do 

 not think a cold temperature kills the bacteria, but I think it numbs them. I 

 think a boiling temperature kills the bacteria, and J think a mr^derate tempera- 

 ture increases the growth of the bacteria." 



.Successful microscopical work was done with magnifying powers of about .000 

 diameters. Pure cultures of spherical-, rod-, and spiral-shaped bacteria grow- 

 ing in test tubes of gelatin were supplied us by Dr. T. Mitchell Prudden of the 



