STERILISATION 99 



fermentation industries. Compared with other acids its antiseptic 

 and germicidal properties are not very pronounced ; thus the bacillus 

 of typhoid fever is killed in five hours by a solution containing 

 0'4 per cent, of lactic acid. Its extensive use in the industries is 

 due to the fact that its presence to a moderate extent in a liquid 

 prevents the growth of a number of obnoxious germs, especially 

 the butyric-acid bacteria. Consequently, in many industries it is 

 found expedient either to inoculate such a liquid with lactic-acid 

 bacteria or to place the liquid in such conditions that lactic-acid 

 bacteria will multiply in it. In either case lactic acid is produced. 

 Of course, in such industries the "souring" must not be allowed 

 to go too far, otherwise the liquid becomes unfit for organisms of 

 any kind to thrive in. The use of lactic acid in the various 

 industries will be dealt with in greater detail when we come to 

 deal with the industries that depend on fermentative processes. 



Salicylic Acid. A two per cent, solution of this acid will destroy 

 pus cocci in about two hours. Koch has tried the effect of this 

 acid on anthrax spores. He dissolved it in oil or in alcohol and 

 found that a five per cent, solution failed to destroy these spores. 

 A 1'6 per cent, solution acting for five hours is sufficient to destroy 

 the typhoid bacillus, and a 1'3 per cent, acting for the same time 

 will do the same to the cholera spirillum. According to Miquel, it 

 is an antiseptic in the proportion of 1 : 1000. In some industries 

 salicylic acid is extensively used to prevent the formation of moulds 

 in such substances as jams, wines, etc. 



Butyric Acid. As a practical disinfectant this substance is out 

 of the question, on account of its exceedingly unpleasant odour 

 of rancid butter, but it has a practical interest for us, because of 

 its possible production, due to the activity of butyric-acid bacteria, 

 in brewing, distilling, butter-making, etc. If it be produced to 

 any extent in a fermenting liquid, the latter is rendered useless. 

 Fortunately, however, the toxic eflFect of butyric acid upon the 

 activity of most bacteria is not great, and though it is without 

 doubt an antiseptic, it is not more so than acetic, lactic, and other 

 comparatively weak acids. Anthrax spores are unaffected even 

 when immersed for five days in pure butyric acid. 



The following table drawn up by Miquel, gives the minimum 

 proportion for each particular substance in which growth of microbes 

 is arrested. He obtained samples of all kinds of germs by collecting 

 them where they were most abundant, viz. from dust of houses, 

 and hospitals, from sewage-water, etc. Broth was inoculated with 



