STERILISATION. 23 



for an hour or more at a pressure of half an atmosphere, 

 corresponding to 112 C. If the object is simply to destroy 

 the pathogenic organisms that are present, especially the 

 tubercular bacilli, it is only necessary, according to Bang and 

 Weigmann, to heat for a few minutes at 85 C., or for a period 

 of from a quarter of an hour to one hour at 65 C. The problem 

 how to secure a product free from any organisms capable of 

 development, and yet of good nutritive value, has not yet 

 been solved, although long-continued treatment at 60 C. has 

 proved of some value. (Absolute certainty cannot, of course, 

 be obtained in this way.) The tendency is, however, to estab- 

 lish a stringent control of the milch cows and of the milking 

 operations, in order to make sure of a healthy product. 



Sterilisation of air can be best secured, as already stated, 

 by means of cotton wool filters. Sulphuric acid or brine 

 baths, cloth filters, etc., are less effective. In the laboratory, 

 where it is often necessary to carry out work in sterile air, 

 glass cupboards are used, the front of which can be sufficiently 

 raised to admit the arms. Some time before using the cup- 

 board the whole of the inner surface is washed over with either 

 mercuric chloride solution or 60 per cent, alcohol, and the 

 cupboard is then closed. Any particles and germs floating in 

 the air will sink to the moist floor, and will be retained there. 



In breweries and other branches of the fermentation 

 industry, the fermentable liquid is sterile at a particular 

 stage in the manufacture, at the moment when the boiling is 

 completed. After the zymotechnical analysis of air had 

 shown that it may convey disease germs to the fermenting 

 liquid, attempts were made to protect the wort during the 

 cooling operation against such infection by the use of closed 

 cooling and aerating apparatus, closed fermenting vats, and 

 storage casks, and by the sterilisation of the incoming air 

 through cotton wool filters. These precautions, together with 

 the use of an absolutely pure yeast, should, theoretically, pro- 

 duce an absolutely pure product. Incidentally, one important 

 practical object was secured, for by blowing in a powerful 

 stream of air during the fermentation, and by the removal of 

 carbon dioxide, the rate of fermenting was greatly increased, 

 and an earlier clearing of the liquor took place. The difficult 



