422 



STATE BOARD OF AGRICULTURE. 



cells are bejjinning to die off. This fact seems, partially at least, to 

 account for the exteudiug of the life and activity of the lactic bacteria 

 in mixed culture, the yeast by its acid-reducing power removing suffi- 

 cient acid so that a certain percentage, if not all, of the lactic 

 microorganisms may continue to retain their optimum fermenting 

 power. 



The acid-reducing power of the yeast LZ was tested in a slightly dif 

 ferent way with comparable results. It was grown with 44 day old 

 pure cultures (milk) of the following different lactic organisms, Strain 

 4, a weak lactic bacterium, No. 3Cb, an organism similar to No. 4, 

 Boct. hulgaricum isolated from yoghourt and No. 53B2. a high-acid- 

 producing organism. These pure cultures were titrated, then inoculated 

 with a loopful of a comparatively fresh culture of yeast LZ. The first 

 two lactic bacteria named were not alive, due to the long sojourn in 

 their own products. Within days, the yeast LZ appeared in the tlask 

 containing No. 3Cb, the presence of the yeast being ascertained by the 

 appearance of the red color; 2 days later, the yeast appeared in Strain 

 4, and 12 days after inoculating the milk, a good growth was present 

 in Nos. 4 and 3Cb, while no growth whatever was apparent to the 

 naked eye in the flasks containing the high-acid lactic bacteria; at this 

 time, these latter flasks were reinoculated with a loopful of one of the 

 cultures of LZ which had been growing in artificially acid whey, under 

 the supposition that this culture of the yeast had become inured to a 

 higher percentage of acid than the first culture used, but on account 

 of the high acidity of the lactic culture or to the small amount of inocu- 

 lum, the yeast never grew in these cultures. The following table shows 

 the acidity in the four cultures after the yeast LZ was introduced : 



TABLE V. 

 Acid Reduction by Yeast LZ — Demonslraled by Growth in Milk Acidified through the Agency of Ladic Bacleria. 



*At this time a larger inoculum of LZ was iotroduced. No growth of the yeast resulted. 



Either the casein in the milk or the products of the lactic organisms 

 derived through the presence of the casein have some stimulating in- 

 fluence upon the yeast LZ. Comparing Tables IV and V, it will be 

 noted that while 20 days elapsed in the LZ culture of -\-00° whey before 

 any growth whatsoever became apparent, abundant growth occurred 

 within G days in Iho milk which had attained a much higher acidity, 

 viz., -|-114°, Ihrough the action of lactic bacteria. 



