338 



NATURE 



[January 12, 191 1 



Out of 138 explosions there were : — 



21 explosions when the barometer stood bet ween 29 -oand 29 49 in, 



56 „ „ ,, 29'5 „ 29-99 ,, 



54 „ ., M 300 .. 30-49 » 



7 M .. .. 305 .. 3°'^ '» 



Furthermore, there were : — 



48 explosions when the barometer WiS rising 

 70 ,, ,, ,, tailmg 



20 ,, ,, ,, sicady or slightly fluc- 



lUiiiin^. 



I also compared the colliery warnings issued in the 

 first half of 1905 with the explosions that took place. 

 'Ihere were in those six months 62 days on which 

 explosions took place out of about 155 working days, 

 so that if a date should be selected at random, the 

 probability that an explosion would occur on that day 

 or the day following would be about 4 to i ; during 

 those six months there were fifteen warnings issued, 

 only six of which were followed within torty-eight 

 hours by an explosion, so that the Press Association 

 only hit upon a dangerous date once in less than ten 

 timies. Obviously it could do better if it trusted 

 to chance alone, and if the matter were not such a 

 serious one, I should be tempted to advise the news- 

 papers concerned to turn over the subject of colliery 

 warnings to their sporting tipsters. Over a series of 

 years the average number of explosions was about 

 150 per annum, and the average number of warnings 

 about 25, so that even if every warning were followed 

 by an explosion, only one explosion in six would have 

 been foretold. 



Of course, it is every explosion that must be taken 

 into account, and not only serious explosions or those 

 attended by loss of life. Whether a small gas explo- 

 sion occurs doing no damage at all, or whether the 

 explosion extends throughout the whole of a colliery, 

 killing its hundreds, is obviously determined by 

 the circumstances of the case, and is indepen- 

 dent of barometric fluctuations ; indeed, modern 

 researches are forcing us very near to the con- 

 clusion that in present-day colliery practice every 

 serious extensive explosion is a coal-dust explosion 

 rather than a gas explosion, though the latter may, 

 and very often does, originate it. In fairness to the 

 news agency, I may point out that when the barometer 

 is high there is a likelihood that the coal-dust in a 

 mine may be drier than when it is low, and it is 

 possible, though not proved, that in these circum- 

 stances the risk of a coal-dust explosion may be some- 

 what greater. This consideration, however, does not 

 affect the general conclusion that the colliery warn- 

 ings as issued by the Press Association, which 

 pointedly refer to firedamp, are misleading, and 

 would be harmful but for the fact that most colliery 

 managers know too much about the subject to pay 

 any attention to them. 



I hold that it would be a real service to the mining 

 community if the Meteorological Office would send 

 out notice whenever an area of considerable baro- 

 metric depression is approaching our shores as long 

 in advance as possible, so as to w^arn colliery managers 

 to be on the look out for a fall in the barometer. 



I understand that similar predictions are furnished 

 to farmers at harvest time for a small fee, and surely 

 if this can be done where material interests alone 

 are involved, it is not too much to ask for the like 

 assistance where men's lives are at stake. It is not 

 at all certain that the influence of barometric changes 

 upon the possibility of colliery explosions is of any 

 great importance, but in matters of such supreme 

 gravity, no precaution, however trifling, should be 

 neglected. Henry Louis. 



NO. 2150, VOL. 85] 



SOURED MILK AND ITS PREPARATION. 

 LACTIC CHEESES. 



IN a former article ^ the nature, preparation, and 

 uses of soured milk were dealt with. It was 

 pointed out that the consumption of sour milk is wide- 

 spread in the East, that in all the sour milks a pecu- 

 liar niTicro-organism is present, with artificial cultun < 

 of which it is possible to prepare soured milk in imita- 

 tion of the natural product, and that soured milk tends 

 to lessen intestinal putrefaction and seems to be bene- 

 ficial in many complaints. The micro-organism 

 {Bacillus bulgaricus) present in all the natural sour 

 milks is one possessing distinct and special character- 

 istics, though exhibiting marked variation or "pleo- 

 morphism," and Makrinoff,^ who has critically studied 

 the question, believes that all the varieties which 

 have been described are referable to one species. Two 

 more or less distinct races seem to exist, namely, one 

 that produces a somewhat viscous product, another 

 that does not, and for the preparation of soured milk 

 the latter is to be preferred as yielding a more palat- 

 able product. The morphological and staining char- 

 acters of the Bacillus bulgaricus are so distinctive that: 



Fig. I. — Filro of properly soured milk, showing presence of the 

 B, bulgaricus only (Gram, X 1200). 



a microscopical examination, combined with the Gram 

 staining process, of the soured milk, enables us to 

 judge to what extent the B. bulgaricus has developed, 

 and whether there is contamination with other organ- 

 isms (Figs. I and 2). 



For the preparation of soured milk it was pointed 

 out that the milk must be properly sterilised by 

 adequate boiling, inoculated with a proper " starter," 

 that is a culture of the B. bulgaricus, and incubated for 

 from 12 to 24 hours at a temperature of 105° to no 

 F. Starters may be obtained in the liquid and sohd 

 (tablet) forms, but unquestionably the liquid are_ far 

 superior to the solid ones. Thus Quant ^ examined 

 certain tablet preparations, and compared them with 

 a liquid culture as regards flavour of, and production 

 of lactic acid in, the .soured milk produced. The 

 liquid culture produced 2-34 per cent, of lactic acid 

 B.P./ the tablets yielded only 007 to 0*42 per cent, 

 of lactic acid B.P. ; moreover, the curd and flavour 

 were unsatisfactory with the latter. Quant also 



1 Nature, April 7, 1910, p. 159. 



2 Centr.f. Bakt., Abt. ii., Pd. xxvi.. 1910, p. 374- 



3 Brit. Med. Journ., 1909, ii., p. 1738. 



4 i?./'. = British Pharmacopoeia. 



