844 , REPORT— 1897. 



tanning involves bacterial actions, owing to wbicli the hair and epidermal cover- 

 ings 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 tanners add the souring 

 liquor of other vats to encourage the souring 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 cer- 

 tain 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. 



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



Probably no other subject in this domain has, however, attained so much im- 

 portance as the bacteriology of the dairy — the study of the bacteria found in milk, 

 butter, and cheese in their various forms. In all cases of this kind, as in brewing, 

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

 tions : 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 possible pathogenic bacteria, i.e., pathogenic to 

 man, which may lurk in the product. 



Of milk especially much has been said as a disease-transmitting medium, and 

 with good reason, as is well known ; and if we may accept the statement of a Con- 

 tinental 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 bring about undesirable or abnormal pro- 

 cesses in the dairy ; but I want to call your attention to the splendid field for 

 bacteriological 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 mUk, culminating 

 in Pasteur's discovery of the bacteria of lactic fermentation in 1857-68. 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 Wiegmann 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 



