160 THE PRESERVATION OP MILK 



127. The Content of Pathogenic Germs in Various 

 Dairy Products. 



A few words must be devoted to the description of the treatment of skim- 

 milk in the factories of Dairy Associations. As is well known, a large portion 

 of the fresh milk sent to the dairy is not sold as such, but is employed for 

 butter-making. The skim-milk formed in large quantities during this process is, 

 in many instances, partly sold per se, and partly worked up into semi-fat and 

 skim-cheese, milk-bread, and the like. In other cases, the contracts made with 

 the membets of the association stipulate that each shall have returned to him, 

 for feeding purposes, a quantity of skim-milk proportional to his deliveries of 

 new. Now, since in these large dairies the cream is removed from the milk by 

 means of the centrifugal machine, it follows that the milk from all sources 

 becomes intimately mixed up together, and consequently if any one parcel of the 

 milk is contaminated, the whole of the skim-milk will become infected thereby. 

 In this manner an epidemic hitherto confined to a single farm may, by means of 

 the returned skim-milk, be rapidly disseminated to all the other cowkeepers. 

 This has actually been frequently proved in respect of the foot-and-mouth 

 disease. In this connection there is an increase in the number of supporters of 

 legislative action in favour of a compulsory heating of the skim-milk returned by 

 dairies to the farmers. As reported by P. VIETH (I.), a Ministerial ordinance 

 has been in force in Prussia since 1894, prescribing that the skim-milk from 

 cows suffering from infectious diseases shall be either kept at a temperature 

 of 90 C. for at least a quarter of an hour, or be heated up to 100 C. before 

 being allowed to leave the dairy. 



It is imperatively necessary that the cream destined for butter-making 

 should be freed from pathogenic germs. According to the concordant results of 

 the researches of L. HEIM (IV.), G. GASPERINI (II.), and O. ROTH (I.), the active 

 organisms of cholera, typhus, and tuberculosis present in the butter long retain 

 their vitality and power. Now, a large proportion of the butter made is con- 

 sumed in a raw state in the form of bread and butter and the like, and if it has 

 been derived from milk or cream infected with pathogenic bacteria, its consump- 

 tion is attended with great danger. Consequently a reliable preliminary 

 treatment of the cream to ensure the removal of these germs is in the highest 

 degree desirable. That this can be practically accomplished will be shown in 

 chapter xxiii. which treats of the artificial souring of cream. 



The same requisition should also be imposed in the case of milk den'gned for 

 cheese-making, but at present this can hardly be effected, because the treatment 

 required for killing the pathogenic germs lessens the suitability of the milk for 

 the purpose in view, and also modifies the flora of the milk to such an extent as 

 to unfavourably influence the ripening process of the cheese prepared therefrom. 

 In fact, until we are in a position to introduce and carry on this process to its 

 completion in a reliable manner by artificially added ferments, the above-named 

 requirement must necessarily remain unfulfilled. Fortunately the acid produced 

 by the ripening process forms an effective antidote, which checks the develop- 

 ment of the pathogenic organisms. H. WEIGMANN and G. ZIRN (I.) proved 

 that Bacillus (vibrio) cholerce asiaticce perished within twenty four hours when 

 artificially inoculated on cheese. 



As will be gathered from the preceding observations, the sterilising of milk 

 samples destined for the cultivation of organh-ms in the laboratory is a very 

 troublesome operation, since this necessitates an absolute freedom from germs. 

 In order to obtain this result, the samples are exposed for ten to fifteen minutes 

 to steam under pressure, at a temperature of 120 C. The decompositions 



