BY R. UREIG-SillTH. 



87 



tlu' lial)ilit.v oL' weak taiining' cud liiiuors to become ropy \vill depend ui(u:i the 

 taunie acid, for the tannins will have become liydrolysed by bacterial action to 

 glucose and tannic acid. Thus afresh liquor with asp. g. of, say, 1.02-i, con- 

 taining about 5'^r of tannin will be quite different in its action to an old liquui 

 of the same gra\ity containing perhaps 5 % of tannic acid. Again, it has been 

 shown that certain salts, notably acetates, prohibit the growth of the rope- 

 forming l)aeteria. Acetic acid is a very common by-product of bacterial activity, 

 and may follow up the alcoholic fermentation should yeasts become active in the 

 liciuors. If acetates are present in the spent liquors they will have a decided 

 influence in preventing the development of ropiness. The matter is therefore 

 complicated; so much will depend upon the composition of the li(|uoi'. 



Once the ropiness is formed in infusions still in contact with the bark, it 

 does not disappear even although the concentration of tannin becomes greater 

 than that necessary to coagulate the slime. Under similar conditions in synthetic 

 media, or in infusions out of contact with (lie bark, tlie riipiness disappears either 

 through coagulation or digestion. 



The acidity of the infusion doubtless jilays a part in promoting ropiness. 

 This was the case with synthetic media which with some phases of the organisms 

 gave most ropiness when the acidity varied from -|-8 to -|-12°, or when it con- 

 tained from 0.75 % to 1 % of tannic acid. In opposition to thi^, the bacteria when 

 grown in the presence of chalk and, thei-efore, in a neutral medium, produced 

 ropiness at 28°, and not at 37° . 



But the main condition is the presence of a sugar and of tlie many that were 

 tested, galactose was the most efficient in promoting the formation of uuieus. 

 Levulose, saccharose, dextrose and the non-sugars, matniit and glycerin were 

 nearly as good, while maltose, lactose and raffinose wei-e iucaiiable of assisting 

 the slime-forming function. 



The nature of the salts did not ajjpeaa' to have nuu-li lutluence when sufh- 

 cient sugar was present. But with a detieieney of sugar (1 %) or with a feeble 

 bacterium, the salt may play a part. Acetates and nitrates prevented the j;rowth 

 of the acti\-e bacteria, and they give us a means of preventing the development 

 of ropiness in bark infusions and presumably in tanning liq»iors. Three poimds 

 of acetate of soda to 1,000 gallons of the water used in making the extract will - 

 prevent the development of ropiness. 



So far as the nitrogenous food is concerned, it did not seem to matter much 

 wnetber meat-extract, peptone, asparagin or ammonium sulphate was used. 

 Nitrates in alkaline solution will also serve, but in the presence of acid or what 

 comes to the same thing, in the presence of sugar, they prohibit growth. 



The ropy substance itself is a galactan, and by the hydrolytie action of sul- 

 phuric acid is converted to galactose. The insoluble slime swells u]i enormously 

 with water, and in common with most insoluble gums, can be liquefied by heat- 

 ing under pressure in contact with a small quantity of sulphuric acid (-\-5°). 



Certain l)y-producfs are formed l)y the bacteria when growing in solutions of 

 dextrose and saccharose in the presence of chalk. These consist of ethyl alcohol, 

 succinic acid, a mixture of fatty acids, all in small amounts, and acetic and fer- 

 mentation lactic acids. The lactic acid preponderates. In addition to these, 

 which are formed by both bacteria, Bacterinm B produces paralactic acid. 



Other differences between the bacteria A and B are that B does not seem to 

 Ite able to utilise glycerin, and its insohible phase, as compared with A. is verv 

 stable . 



