[ 755 ] 



hands and the pail properly, there are much fewer microbes. 

 The last strippings of milk are free from microbes. 



1,305. The Bacillus lactis converts milk-sugar into lactic 

 acid. As this ferment is the agent for curdling milk into 

 dahi^ and as dahis are apt to get more or less improperly 

 curdled, the conditions required for the most perfect curdling 

 of dahi should be understood. The sanjo i. e. the seed or cul- 

 ture, should be made of skim-milk and not rich milk, as it is not 

 desirable to associate the butyric ferments with the lactic. 

 The skim-milk should be taken in the fresh state, heated to 

 about 75 C to pasteurise it, i. e. } to temporarily kill all the 

 germs and then, after adding a little watery portion of any 

 dcihi, to leave the pasteurised and inoculated skim-milk 

 in a cool place, i.e. } at a temperature of about i6C. This 

 can be used afterwards as souring agent for making good 

 dahi or for souring cream before churning it into butter. 

 We often find dahi of a slimy character. This is due to a 

 micrococcus attacking the milk-sugar in larger numbers and 

 replacing or resisting the action of the lactic bacilli. This 

 micrococcus multiplying becomes a zooglcea, and the sttme 

 is a zooglcea-slime. There are other characteristics we 

 notice in dahi, the most noticeable of which are coloured 

 patches on the surface of pots of bazaar dahi. The 

 blue patches are due to Bacillus cyanogenus, the yellow 

 patches to Bacillus synxanthus; and the blood-red patches 

 to Micrococcus prodigiosus. There is a Sarcina which pro- 

 duces rose and another which produces bro'wn red, colour, and 

 Bacteria lactis erythrogenes while coagulating milk like 

 Bacillus acidi lactis imparts to it a blood-red colour if light 

 be excluded. These chromogenic microbes which are fairly 

 common in milk, are not known to produce disease, though 

 the blood-red colouration produces a superstitious horror 

 which induces owners of valuable cows to part with them 

 at once, as they do not know the cause of the blood-red 

 colouration was not present in the cow at all, but in impuri- 



