t6o 



NATURE 



[Apkil 7, 19 lo 



perature (99° F.) and maintain itself in spite of the 

 competition of the other micro-organisms present. 

 The ordinary lactic acid ferments found in milk grow 

 best at 75°-85° F., and are unsuitable. 



Metchnikoff says' " I had no illusion as to the diffi- 

 culty sure to be encountered in any effort to introduce 

 lactic microbes into the intestinal flora which has been 

 preoccupied by a multitude of other microbes. To make 

 surer of the result, I chose the lactic microbe which is 

 the strongest as an acid producer. It is found in the 

 Yoghurt, which originates in Bulgaria. The same 

 bacillus has also been isolated from the leben of 

 Egypt ; and it is now proved that it is found in the 

 curdled milk of the whole Balkan peninsula, and even 

 in the Don region of Russia." Metchnikoff also noted 

 that some of those who consumed a diet of little else 

 than the soured milk lived to an advanced age. This 

 then was the origin of the use of Bulgarian sour milk, 

 and of the introduction of artificial substitutes for the 

 natural article. It may be added that the use of sour 

 milk seems to be widespread in the East, for it is 

 found also in Turkey, Siberia, and Asia Minor, and 

 in India under the name of " Dadhi."^ As Chaterjee 

 says, "The extensive use of one or other varieties of 

 fermented milk, produced by means of a special fer- 

 ment in Eastern countries, probably owes its origin 

 to the difficulty of preserving milk in a sweet condition 

 for a long time, in comparison to cold countries ; 

 milk when undergoing spontaneous decomposition in 

 hot climates becomes changed within a few hours to 

 a foul-smelling fluid in which the casein and the fat 

 have undergone liquefaction, whereas, when fer- 

 mented by means of the special ferment the decom- 

 posing, gas-producing, proteolytic bacilli are killed off 

 by the more vigorous organism of the ferment, which 

 has no destructive action on the fatty or albuminous 

 constitutents of milk, so that by this means milk can 

 be kept in a condition fit for consumption for a long 

 time." • 



The bacteriology of the various natural sour milks 

 is somewhat complex and not yet fully elucidated, 

 although considerable research has been devoted to it. 

 Micro-organisms of a peculiar type are present in all. 

 One of the first to be isolated was the Bacillus bul- 

 garicus, a large Gram-staining, non-sporing, rod- 

 shaped organism, which grows best at temperatures 

 between 110° F. and 120° F. Development, however, 

 is slow even at the optimum temperature, taking three 

 days for the maximum production of lactic acid in 

 milk, and it is therefore unsuited for the preparation 

 of artificial soured milk. Another organism is the 

 "granule bacillus" (Kornchenbacillus) of Kuntze. 

 This is probably the organism so often spoken of as 

 the "bacillus of Massol," and is widely used for the 

 preparation of soured milk, as it grows rapidly and 

 well at a temperature of about 100° F. and produces 

 a relatively high percentage of lactic acid. The 

 name of "granule bacillus" is derived from 

 the fact that granules which stain deeply are 

 present in the bacterial cell. In all the natural 

 soured milks somewhat similar micro-organisms 

 are to be found. It is of interest that Kuntze 

 has suggested that these Bulgarian lactic fer- 

 ments are allied to the jB. acidophilus and B. bifidus, 

 which, as already stated, are present in the child's 

 intestine, and they are probably primarily of intestinal 

 origin. 



In natural sour milks the special lactic acid fer- 

 ments are always associated with other ordinary lactic 

 acid bacteria, particularly a Streptococcus (S. lacticus), 

 and a mixed culture of this last-named organism with 

 the bacillus of Massol. presents advantages over the 



1 Century Magazine, November, 1909, p. 56. 



- Chaterjee, Ind. Med. Gazette, September, 1909, p. 329. 



NO. 21 10, VOL. 83] 



use of the latter alone.' For instance, when the B. 

 bulgaricus grows alone in milk it has some effect on 

 the fat, producing small quantities of nauseous tasting 

 substances, but Metchnikoff has shown that this result 

 is entirely obviated by a symbiotic growth with an 

 ordinary lactic acid organism. The ingestion of milk 

 soured by an ordinary lactic acid organism also t^nds 

 to produce in the intestine an acid environment which 

 favours the growth and persistence of the special 

 lactic ferment, the bacillus of Massol. 



Various procedures are adopted for the preparation 

 of the natural sour milks. According to one account. 

 Yoghurt is prepared by boiling milk until it has 

 diminished to half its volume by evaporation, it is then 

 allowed to cool somewhat and a little of a previously 

 prepared sour milk is added and the whole allowed to 

 stand in a warm place until next • day. Another 

 method is to wipe round a wooden bowl with a piece 

 of cheese (presumably prepared with the sour milk) 

 and then to introduce into the bowl the boiled milk. 

 Dadhi is prepared by boiling mim for some time, 

 cooling to blood-heat, and then inoculating with a 

 needle dipped in a former brew. The inoculated milk 

 is covered with a blanket and kept in a warm place 

 for 12 hours. 



For the artificial production of soured milks the 

 milk is well boiled in order to sterilise it and destroy 

 undesirable organisms, and when it has cooled suffi- 

 ciently a "starter" consisting of a pure culture of the 

 proper lactic ferments is added. The inoculated milk 

 is then kept at ioo° F. or thereabouts for from lo to 24 

 hours, according to the amount of starter added, and 

 should then be fit for use. Many " starters," both 

 liquid and solid (tablets), are to be had, but only a few 

 are to be recommended, as some are grossly con- 

 taminated with undesirable bacteria. Another method 

 is to add a little of the previous day's preparation to 

 the milk to be soured. .Some of the large dairy com- 

 panies also supply the soured milk ready for consump- 

 tion. 



Considerable care must be exercised in preparation 

 to use sterilised vessels and to safeguard the milk 

 from contamination during incubation. The milk 

 properly prepared should be thoroughly curdled, pos- 

 sess a not unpleasant tart flavour, and have a marked 

 acid reaction. Some of the older "starters" contained 

 sporing bacilli which though they curdled the milk 

 (owing to tryptic ferments) gave rise to little or no 

 acidity. Preparations containing a combination of the 

 bacillus of Massol, with Streptococcus lacticus or 

 lebenis, are probably the most suitable. 



The internal administration of tablets, &c., contain- 

 ing the lactic ferments, in place of the soured milk, 

 is of questionable utility. 



Although some are still sceptical as to the value of 

 soured milk, it can hardly be doubted that it is 

 beneficial in many complaints.^ Among these are (a) 

 those depending on abnormal putrefaction of proteins 

 in the intestinal tract, and including certain cases of 

 acute enteritis and acute and chronic colitis ; (b) auto- 

 intoxication, with products of intestinal putrefaction, 

 as in many cases of general failure of health in elderly 

 persons, forms of anaemia, neurasthenia, with 

 flatulent dyspepsia, &c. ; in minor ailments such as 

 lassitude, headache, some forms of constipation and 

 diarrhoea, rheumatic pains, and the like, benefit fre 

 quently results. It must also be recognised that even 

 if the soured milk as such does little good, it often 

 enables an addition of valuable and easily assimilable 



1 "On the Bacteriology of Yoghurt," &c., see Luerssen and Kfihn, 

 CentralH. f. Bakt., Abt. ii , xx., 190S, p. 234; Kuntze, ib., xxi.. 1908, 

 P- 737 » White and Avery, ib., xxv., 1909, p. 161 ; Hastings and Hammer, 

 ib., XXV., 1909, p. 419. Full references to the literature of the subject are 

 given in these papers. 



^ Herschel, Proc. Roy. Soc. Med., January, 1910. 



