THE DILUTION METHOD. 127 



beer. In each of the first fifteen flasks in both series is placed 

 one drop (0.04-0.05 c.c.), and in each of the remaining flasks 

 0.25 c.c., of the water to be tested. These fifty flasks are then 

 kept at a temperature of 2 4 -2 5 C. for fourteen days, and are 

 examined to ascertain how many become turbid or throw up a skin, 

 i.e. exhibit signs of the development of organisms. The ratio of 

 the number of flasks with turbid contents to the total number is 

 referred to i c.c. of water, and a standard for determining the 

 destructive capacity of the sample in question is thus obtained. 

 Assuming that, for instance, three out of the fifteen wort-flasks 

 (inoculated with 0.04 c.c.) exhibit turbidity, then three growths 

 have proceeded from 15 x 0.04 c.c., or live from i c.c. of the 

 water. Or, on the other hand, suppose that of the beer-flasks 

 only one has become turbid, and that this is one inoculated 

 with 0.25 c.c. In this case, then, there is but one growth per 

 10 x 0.25 = 2.5 c.c. 



H. WICHMANN (II.) attempted to add, as a co-factor influencing 

 the conclusion arrived at, the length of time required for the 

 turbidity to develop; of this fuller particulars will be found in 

 the reference just given. Hansen showed that a large number 

 of species of water-bacteria are incapable of developing in the 

 two solutions last named, and this is particularly the case with 

 beer, the flasks charged therewith seldom becoming turbid after 

 inoculation with water. J. CH. HOLM (I.) has, for several con- 

 secutive years, regularly examined the well-water and main-water 

 of the breweries at Alt-Carlsberg near Copenhagen by this method, 

 and found that the spores of mould-fungi are comparatively 

 the most frequent, cells of bacteria capable of thriving in wort 

 and beer being less general, and yeast cells very rare. If the 

 water be used merely for malting and mashing purposes, its germs 

 -are unimportant, being, as we have already seen, unable to with- 

 stand boiling in the hop-copper. There is, however, one unavoidable 

 opportunity afforded for the contact of the beer with the water in 

 its unchanged condition, and that is in the washing out of the 

 storage casks and of the trade casks in which the beer is sent out 

 to customers. In Germany these casks, being lined with pitch, 

 will not stand cleaning with hot water or steam, and are cleaned 

 with cold water, a small quantity of which is always left behind 

 in the casks ; so that, if this water be rich in organisms injurious 

 to beer, serious inconveniences may arise. Dr. Will has reported 

 to the author an instance coming under his knowledge where the 

 beer from a brewery was constantly so turbid that no customers 

 would take it. After prolonged investigation the cause was 

 eventually discovered in the well-water, used for swilling out 

 the casks, which was found to be rich in the organisms producing 

 turbidity in beer. Subsequent examination showed that the well 

 was connected with the drains by means of fissures in the soil. 



