328 MILK AND ITS HYGIENIC RELATIONS 



In this country there is still a section of people who cling to the 

 belief in the ' vital ' properties of milk (said to be destroyed by heat) 

 as essential elements in the successful feeding of infants. The results 

 obtained all around them by the use of pasteurised, boiled, or dried 

 milk fail to convince them of the absence of such properties. 



Doubtless much of this attitude of mind arises from the fact that 

 the scientific literature dealing with the subject is for the most part 

 in foreign periodicals, and the pressure of daily life does not encourage 

 acquaintance with the results obtained by other methods. 



This sentiment has recently found expression in an experiment 

 conducted by the Liverpool Corporation to sterilise milk used at their 

 infant milk depots by electricity. The work was carried out by 

 Prof. Beattie and his assistants, and the results investigated from 

 various standpoints. 



There seems no doubt that the method is entirely satisfactory in 

 destroying as high a percentage of bacteria as is effected by pasteurisa- 

 tion. The report made to the City of Liverpool in 1914 showed, that 

 over a period of fifteen days the percentage of bacteria destroyed 

 reached an average of 99*93 per cent. Special mention is made of the 

 destruction of the acid-forming organisms ; and tubercle bacilli were 

 destroyed in some experiments in which the organisms had been 

 added to he milk. The milk is said to keep extremely well after the 

 treatment, and it is further ^claimed that the ' enzymes are not 

 destroyed.' The nature of ffche enzymes is not stated, but in view 

 of the experiences already recorded in the previous pages, the whole 

 question is immaterial. 



The more important features ofj the method are shown in 

 Plate VIII. 



The milk is poured into a large tank and is passed gradually into 

 the ' lethal ' tube. The rate of passage is regulated to ensure a 

 sufficient duration of the treatment. After passing through the tube 

 the milk is at once bottled. 



The re-contamination of the milk must be avoided as in the case 

 of pasteurised milk, and the bottles must be cleaned and sterilised as 

 in the case of pasteurisation. There is however the added risk of 

 contamination during manipulation, which risk has been found to be a 

 very real one, and has led to the abandonment of the method at the 

 milk depots. 



It is possible that this method might be of value for commercial 

 purposes. As, however, the plant is expensive, and must be worked 

 by a competent engineer (owing to the high electric potential of the 

 currents used and to the complicated apparatus) , it is unlikely, in view 

 also of the cost of the electric current, that this would be found cheaper 

 than the use of heat. 



Another method has recently been introduced in Germany, and 

 has proved a source of much discussion. The apparatus, which is 

 known as the ' Biorisator,' consists of a double-walled chamber, the 

 milk being heated by means of steam at 75 C. The milk is passed 

 in, in a fine jet in the form of a spray and is said to retain all 

 the properties of raw milk. The discussion arose between various 

 investigators who were unable to find much reduction in the bacterial 

 content in the milk stated to have been purified by this method. It 

 seemed probable that here also a difficulty had arisen in regard to 



