294 FILTRATION AND HEATING OF MILK 



The sterilization of milk in this way has not become 

 a popular process, partly because of the trouble and 

 expense involved, but mainly on account of the altera- 

 tion in flavour which results. The taste of boiled milk 

 is very readily recognized, and is disliked by children as 

 well as by adults. Nevertheless, in spite of the dis- 

 advantages and objections to the use of boiled milk, 

 boiling for a short time is the simplest and safest means 

 of getting rid of pathogenic organisms, which, under 

 present conditions of production and distribution, too 

 frequently find their way into the milk supplied to the 

 householder. 



Ex. 141. Pour 250 c.c. of fresh evening's milk into a 

 sterile flask, and allow it to stand in a cool pantry until next 

 morning. 



(a) Dilute a small amount of it to i in 1000 with sterile 



water, and prepare two litmus agar plates from it, 

 using .5 c.c. for inoculation. 



(b) Boil 100 c.c. in a flask for five minutes; cool, and 



prepare two litmus lactose agar plates from it as 

 above. 



(c) Plug the flask with cotton-wool and leave it in a room 



at ordinary temperatures for twenty -four hours ; 

 then prepare two litmus agar plates from it as 

 before. 



Incubate all the above at 35 C. for forty-eight 

 hours; note and compare the number of colonies, 

 their form and acidity, which appear on each plate. 



Stain and examine specimens of the organisms 

 from the different colonies. 



(d) Place the unboiled milk remaining in a 100 c.c. flask 



by the side of the boiled sample. 



Leave them until both are curdjed, noting which 

 curdles first, the nature of the curd, the separation 



