SCIENTIFIC PROGRESS

Waipa Post, Volume 52, Issue 3705, 10 January 1936, Page 4

SCIENTIFIC PROGRESS

MODERN STERILISATION. SUCCESS OF NEW PROCESS. The question of the bacterial contamination of water, milk and other products on which man is dependent for his food supply or his beverages has for long engaged the attention of scientific workers in all countries. The problem of the destruction of these bacteria is, in a manner of speaking, twofold, for the organisms may be pothogenic and responsible for disease when ingested or by their entry to the system through mucous membranes or in regions where the skin is broken (as, for example, in the transmission of disease by bathing pools where the water acts as the vehicle for spreading infection). On the other hand, bacteria which are not pathogenic may by their growth in the medium itself be responsible for the deterioration of the material. The destruction of the pathogenic bacteria must be ensured to protect the public health, and the elimination of the others is an economic necessity in guaranteeing the production of a sound and dependable commodity. USE OF CHEMICAL AGENTS. Obviously in an article of such limited scope only a few aspects of the question of sterilisation can be dealt with, and water which enters so universally into our daily life is worthy of first consideration. This may be contaminated in a great variety of ways, and may contain a high count of pathogenic organisms. A degree of sterilisation may be attained by continuing boiling, and this procedure should always be followed in cases of doubtful samples. Chemical agents are, on the whole, more convenient and more effective, and of these the most widely used is the gas chlorine, or compounds, such as bleaching powder, which contain readily available chlorine. A concentration of some three parts per million of chlorine in water is reported to destroy all harmful organisms within 30 minutes. A striking example of the effectiveness of this treatment is found in the comparison of the health of the troops engaged in the South African war and in the Great War. During the former campaign the incidence of enteric fever, clue to infected water supplies, was remarkably great, and the extent of such casualties presented a worrying problem. During the fourteen years that elapsed before the outbreak of the Great War, a system of chemical sterilisation suitable for field work was developed with the result that casualties from enteric during the latter campaign were negligible. The system was simple, a treatment unit being conveniently mounted on a motor lorry. This consisted of a series of tanks, into the first of which water from the river or pool was pumped, and the requisite amount of chlorine introduced from a cylinder of the compressed gas. After a lapse of the required time the excess chlorine was destroyed by the addition of the calculated amount of sulphur dioxide, or sedium and the water, after filtration through a chamber packed with sand, was collected in a storage tank for use. Such water, although perfectly reliable, is not altogether free from objectionable taste. Chlorine treatment was also very generally adopted for the purification of water for swimming pools, and in this case if the excess chlorine is not carefully neutralised, the water may have a very irritating effect on the eyes and the membrane of the nasal cavity. MODERN PROCESS. This method of sterilisation of water has now been superseded by a modern process which is not only more effective but is also free from the objections due to the introduction of chlorine. This is known as the oligo-dynamic or electro-catadyne process, and the necessary plant for treating water and other materials such as wine and dairy products (which are at present partially sterilised by pasteurisation processes) is available from manufacturers such as the Siemens Schuckert firm.

In this process advantage is taken of an Interesting biological property of silver which has been known for almost 50 years—its effect on bacterial life. Silver and certain other metals are found to possess what is known as oligo-dynamic action, which simply means that in solution in water exceedingly small traces of these metals are able to destroy any existing bacteria, and moreover the water is rendered resistant to further bacterial contamination. This property is possessed by silver in a marked degree, and it is by far the most bacteriacidal of all the metals. The amount of silver in solution which is sufficient to exhibit this oligo-dynamic action is extraordinarily small, amounting to one part per thousand million parts. This amount, of course, is beyond the limits which can be detected by ordinary analytical methcds. It is not yet definitely known of what the bacteriacidal property depends, but by some authorities it is contended that the action is connected with a film of active oxygen absorbed on the surface of the silver ions, and that these are capable of absorption on the surfaces of the