024 



NATURE 



[February 6, 19 13 



to bacterial growth and development. It is true 

 tliat Avres and Johnson have stated, as a result 

 of their experimonls on milk pasteurised at 145° F. 

 for 30 minutes or at 160° F. "flash," that the 

 resultant milk sours similarly to raw milk, and 

 that the relative numbers of the various organisms 

 remain unchanged. 



Apart from the fact that these temperatures are 

 probably untrustworthy for killing- the tubercle 

 bacillus, it is necessary to point out that, thoug^h 

 the relative proportions of the organisms may be 

 unaltered by this treatment, it by no means follows 

 that the actual species remain the same, for the 

 predominant lactic-acid organism {Streptococcus 

 lacticus or Giintheri) certainly succumbs at these 

 temperatures. In any event, the subsequent bac- 

 terial content of pasteurised milk depends not only 

 on the pasteurising temperature, but also on the 

 temperature at which it is subsequently kept. 

 Milk pasteurised at a temperature above 165° F. 

 for any time, and afterwards kept at a tempera- 

 ture above 65° F., always underg-oes what may 

 be termed a "peptolytic" change, allied to putre- 

 faction, and the latter may actually occur if 

 pasteurisation has been conducted at I70°-I75° F. 



With pasteurisation at these higher tempera- 

 tures, this "peptolytic" change may take place 

 without at first apparent alteration in the milk. 

 These changes, however, do not take place if the 

 milk, after pasteurisation, be kept below 50° F., 

 and this is the crux of the matter so far as the 

 bacterial content is concerned. The real danger 

 of pasteurised milk arises from the fact that the 

 milk is stored by the consumer in warm pantries, 

 or is purposely kept hot in vacuum flasks or food- 

 warmers for infant or invalid feeding ! A similar 

 danger may ensue if, as is frequently done, the 

 milk be boiled and allowed to cool spontaneously. 

 It is notorious that summer diarrhoea in children 

 coincides with the period when room-temperatures 

 of 70° F. and upwards prevail, and when the 

 necessity for boiling the milk is considered to be 

 greatest, the proper cooling and protection of 

 such boiled milk being completely overlooked and 

 omitted ! The work of Dr. Ralph Vincent in 

 this connection is strongly confirmative of this 

 view. 



There can be no doubt that summer diarrhoja 

 of children is not due to an excessive development 

 of the true lactic-acid-producers, tor the adminis- 

 tration of soured milk or whey is often of service 

 in the treatment of the condition, and soured 

 milk containing vast numbers of these organisms 

 is a valued article of diet in all parts of the w'orld, 

 including the tropics. When summer diarrhn?a 

 occurs after the use of raw uncooked milk, the 

 explanation is that an initially dirty milk has been 

 kept at such a temperature that the peptolytic 

 bacteria have developed more vigorously than the 

 lactic forms, and these organisms or their pro- 

 ducts induce the condition. 



If raw and pasteurised milks be kept at blood- 

 heat until curdling ensues, the character of the 

 curd and the microscopical appearances therein 

 will be found to he cntirciv different, despite the 

 NO. 2258, VOL. 90I 



fact that, even in the raw-milk sample, consider- 

 able proteolysis (though from a different cause) 

 may have taken place. 



If, then, pasteurised milk is to be taken in pre- 

 ference to raw milk, unless consumed at once 

 there seems to be only two ways of safeguarding 

 its use, either (i) to cool immediately and subse- 

 quently to keep it always at a temperature below 

 50° F., which in summer in the household is 

 difficult to ensure, or (2) to add a sufficiency of an 

 active culture of lactic-acid-producing organisms 

 to reproduce the original condition of the raw 

 milk, which may not be altogether practicable.' 

 Similar considerations affect the use of boiled 

 milk. Unless safeguarded, pasteurisation may 

 also lead to less care in the production and dis- 

 tribution of the milk, since obvious change in it 

 occurs more slowly than in untreated milk. There 

 will also be a tendency for the smaller and the 

 less scrupulous dealers to treat dirty or returned 

 milk, and thus to make sure of its ultimate 

 disposal. 



There is no need here to enter into the vexed 

 question of the alteration and diminution in nutri- 

 tive qualities which ensue from heating milk. 

 The lower the temperature of heating the less the 

 alteration, and in this respect pasteurised milk 

 has the advantage over boiled or sterilised milk. 

 R. T. Hewlett. 



NOTES. 

 We announce with regret the death on January 31. 

 at sixty-five vears of age, of the Earl of Crawford, 

 F.R.S., president of the Royal Astronomical Society 

 in 1878-79, and distinguished in the world of science 

 by his work for astronomy. 



A Reuter telegram from Stockholm announces the 

 death, at sixty-seven years of age, of Dr. G. de 

 Laval, the well-known inventor of the steam turbine 

 which bears his name. 



Dr. W. Carter, who for many years was pro- 

 fessor of materia medica and therapeutics in the 

 University of Liverpool, and took a large share in the 

 initiation of the Liverpool School of Tropical Medi- 

 cine, died on February 2 in his seventy-seventh year. 



At the annual general meeting of the Royal Astro- 

 nomical Society, to be held on Friday, February 14, 

 the gold medal of the society will be awarded to 

 M. H. A. Doslandres, for his investigations of solar 

 phenomena and other spectroscopic work, and the 

 Jackson-Gwilt medal and gift to the Rev. T. H. E. C. 

 Espin, for his observations of the spectra of stars and 

 his discovery of Nova Lacertae. 



The annual meeting of the Iron and Steel Institute 

 will be held at the Institution of Mechanical Engineers, 

 Storey's Gate, Westminster, on Thursday and Friday, 

 May I and 2. The Bessemer gold medal will be 

 awarded to Mr. Adolphe Greiner, general director of 

 the Soci6t6 Cockcrill, Scraing, vice-president of the 

 institute. The autumn meeting will be held at 

 Brussels, at a date to be announced later. 



