September i6, 1897] 



NATURE 



477 



claimed that the flavour of European-grown tobacco can be 

 materially improved by its use. I read that the process is 

 patented, which may or may not affect its value as a scientific 

 announcement; but in view of the increasing number of re- 

 searches into this subject by Behrens, Davalos, Schloesing, and 

 others, it is evidently a domain for further bacteriological 

 investigations in a properly equipped laboratory. 



Every botanist knows that flax and hemp are the bkst fibres of 

 Lhmm and Cannabis respectively, separated by steeping in 

 water until the middle lamella is destroyed and the fibres 

 isolated ; but it is perhaps not so well known that not every 

 water is suitable for this " retting" or steeping process, and for 

 a long time this was as much a mystery as why some waters are 

 better than others for brewing. 



Only quite recently Fribes, working under Winogradsky, has 

 isolated the bacillus which accomplishes this dissolution of the 

 middle lamella, and its behaviour brings to light some very 

 interesting details, and furnishes another of those cases where 

 J the reactions of living micro-organisms can be utilised in deciding 

 questions of plant chemistry too subtle for testing with ordinary 

 reagents. 



Vou are aware that recent researches, especially those of 

 Maquin in France and of Walter Gardiner in Cambridge, 

 Cross and Bevan and others, have caused us to discard the view 

 that the middle lamella is composed of cellulose, and to learn 

 that it consists of pectin compounds. Now Fribes' anaerobic 

 bacillus dissolves and destroys pectins and pectinates, but does 

 not touch cellulose or gum, and thus enables us to criticise 

 from a new point of view the Ijacillus {B. Atnylobacter) which 

 Van Tieghem asserted to be the cause of cellulose fermentation 

 and the retting of flax. Ciearly it cannot be both, otherwise 

 the flax-fibre would be destroyed ; and we know from other facts 

 that B. Amylobacter is not the cellulose ferment. 



Fribes' discovery has yet to be tested with reference to other 

 processes of retting. The Indian Government have lately pub- 

 lished a series of notes on jute and other fibres, and the descrip- 

 tion of the retting of jute suggests this as a very definite problem 

 for investigation. 



I am told that a patent exists in the United States for a 

 process whereby the retting organisms may be sown and 

 encouraged in waters otherwise unfitted for the steeping of flax, 

 <S:c., another indication of the keen interest taken in these 

 matters. 



It goes without saying that the steeping of skins in water in 

 ]ireparation for tanning involves bacterial actions, owing to 

 which the hair and epidermal coverings are removed ; but it 

 appears from recent investigations that in the process of swelling 

 the limed skins, the gases evolved in the substance of the 

 tissues, and the evolution of which causes the swelling and 

 loosens the fibre so that the tanning solutions may penetrate, are 

 due to a particular fermentation, caused by a bacterium which, 

 according to Wood and Wilcox, is similar to, if not identical 

 with, a lactic ferment. If Haenlein's results may be accepted, 

 it is a bacillus introduced into the tanning solution by the pine 

 bark, which is responsible for the advantageous acidification of 

 the tanning solutions much valued for making certain kinds of 

 leather, and of decisive importance in the quality, so that 

 ' inners add the souring liqour of other vats to encourage the 

 luring of the doubtful one. 



Hay is made in very different ways in different countries, and 

 in those where a "spontaneous" heating process is resorted to 

 there seems to be no doubt that certain thermogenic bacteria are 

 concerned. The researches of Bohmer, Dietrich, Fry, Lafar, 

 and others show that here and in the preparation of ensilage we 

 have important fermentation processes which affect the end result. 

 r The whole question of fermentation in hay, and the high 



' temperatures produced in the process, as well as what occurs 



in straw-stacks under similar conditions, have important theo- 

 retical bearings, and we know of bacilli which grow at 70° C. 



Probably no other subject in this domain has, however, 

 itained so much importance as the bacteriology of the dairy — 

 the study of the bacteria found in milk, butter, and cheese in 

 I heir various forms. In all cases of this kind, as in brewing, 

 bread-making, and so on, there are three aspects of the bacteri- 

 ology of the operations : we have to consider first the bacteria 

 concerned in the normal process ; secondly, introduced forms 

 which bring about abnormalities, or "diseases" of the normal 

 operation ; and, thirdly, the ix)ssible pathogenic bacteria, i.e. 

 l^athogenic to man, which may lurk in the product. 



Of milk especially much has been said as a disease-trans- 



NO. 1455, VOL. 56] 



mitting medium, and with good reason, as is well known ; and 

 if we may accept the statement of a continental authority, who 

 calculated that each time we eat a slice of bread and butter we 

 devour a number of bacteria equal to the population of Europe, 

 we have grounds for demanding information as to what these 

 bacteria are, and what they are doing. And similarly with 

 cheese, every kind of which teems with millions of these minute 

 organisms. 



Now I cannot, of course, go into the question of pathogenic 

 bacteria, nor is there time to discuss those forms which Ijring 

 about undesirable or abnormal processes in the dairy ; but I 

 want to call your attention to the splendid field for bacterio- 

 logical investigation which is being opened up by inquiries into 

 the normal changes utilised in making butter and cheese. 



We may pass over the old controversies as to the souring of 

 milk, culminating in Pasteur's discovery of the bacteria of lactic 

 fermentation in 1857-58. Lister in 1877 isolated Bacterium 

 lactis. Hueppe in 1884 confirmed his results, and added several 

 other lactic bacteria, and we now know a whole series of forms 

 which can turn milk sour by fermenting its sugar, and this in 

 various ways, as Warington and others have shown. The 

 souring of milk and cream by merely leaving it to stand often 

 led to failure, and the study of this preliminary to butter- and 

 cheese-making is itself a bacteriological question of great 

 importance. We shall not be surprised, therefore, that when, 

 in 1890, Wiegmann proposed to use pure cultures of lactic-acid 

 bacteria for the souring of cream, the plan was at once taken up. 



Some years ago Storch found that the peculiar aroma of a good 

 butter was due to a bacterium which he isolated, and Wieg- 

 mann has now two forms, or races, one of which develops an 

 exquisite flavour and aroma, but the butter keeps badly, while 

 the other develops less aroma, while the butter keeps better. 



According to a recent publication of Conn's, however, this 

 .subject has been advanced considerably in America, for they 

 have isolated and distributed to numerous dairies pure cultures 

 of a particular butter-bacillus which develops the famous " June 

 flavour " hitherto only met with in the butter of certain districts 

 during a short season of the year. I am told that this fine- 

 flavoured butter is now prepared constantly in a hundred or 

 more American dairies. Simultaneously with these advances in 

 the manufacture of pure butter with constant flavour, the days 

 of " diseased " butters seem numbered. 



Properly considered, the manufacture of cheese is a form of 

 microscopic gardening even more complex and more horticul- 

 tural in nature than the brewing of beer. From the outset, when 

 the chee.semaker guards and cools his milk till his stock is ready, 

 he is doing all he knows how to do to keep down the growth 

 of the germs introduced into the milk ; he then coagulates it, 

 usually with rennet— an enzyme of animals, but also common 

 in plants — and the curd thus prepared is simply treated as a 

 medium on which he grows certain fungi and bacteria, with the 

 needful precautions for favouring their development, protecting 

 them against the inroads of animal and plant pests, and against 

 unsuitable temperature, moisture, access of light, and so on. 

 Having succeeded in growing the right plants on his curd, his art 

 then demands that he shall stop their growth at the critical 

 period, and his cheese is ready for market. 



The investigations of Duclaux, Wiegmann, and others on the 

 continent, of Conn in America, and of Lloyd in England, to 

 say nothing of other workers now busy at this subject in various 

 parts of the world, are getting at the particular forms of fungi 

 concerned in so altering the constitution of curd that it becomes 

 the very different article of food we call cheese, and they have 

 even determined to some extent what r6le is played by these 

 plants in giving the peculiar odours and flavours to such different 

 cheeses as Camembert, Stilton, and Roquefort. It is known, 

 for instance, that a certain fungus {Penicillium) cultivated on 

 bread is purposely added to Roquefort, and that it destroys the 

 lactic and other acids, and so enables certain bacteria in the 

 cheese, hitherto inhibited in their actions by these acids, to 

 set to work and further change the medium, whereas in making 

 Emmenthaler cheese the object is to prevent this fungus thus 

 paving the way for these bacteria. Pammel claims to have dis- 

 covered a bacillus which gives a peculiar and much-admired 

 clover aroma to certain cheeses, and according to recent state- 

 ments a definite Streptococcus is responsible for the jjeculiarities 

 of certain Dutch cheeses, and so on. Nevertheless, we are 

 still profoundly ignorant of most of the forms concerned in the 

 ripening of cheese, and every research which throws light on 

 this difficult and complex subject, and so paves the way to 



