BACTERIA.

Waikato Times, Volume 114, Issue 19011, 31 July 1933, Page 10

BACTERIA.

. / RELATION TO DAIRYING. - w ■ POINTS TO BE WATCHED. . 7 ' ? ■ (By ,H. R. Whitehead, D.Sc., Massey : /sj t College, in a lecture delivered at /l the Waikato Farm School.) lY'. aim or tills lecture is to try to $ picture before your mind’s eye those (* J.ihysterious beings—bacteria, germs, or •mlpro-organisms which arc so small that they cannot be seen by the naked : .f ; eye Tiie dairyman will inevitably learn bow to deal more logically with bacteria if he has a clear idea of their nature and can visualise how they •.» Bacteria are the lowest form of , plant life. The consist each of a single cell with little visible structure. The higher plants and animals are built up from millions of cells which vary in nature, and arc adapted to various functions, blit each bacterium \villiiff its single cell carries on a >•: Separate existence. Where do Bacteria Originate? A school Of scientific workers, among whom Pasfepr was outstandlog, showed that wlie^T'-"fluid was

sterilised by heat and then kept in a sealed vessel no bacteria appeared, no matter bow long the liquid was kept. The protagonists of spontaneous generation countered this by postulating that the admission of air was necessary before the germs could be generated. Pasteur, however, was able to show that if a vessel 'containing a boiled fluid was sealed with a pad or cotton-wool or by bending its neck ■in an S shape so that air, but not dust, was admitted, the liquid remained free from bacteria. After many such demonstrations he finally proved conclusively' that the germs were never generated spontaneously in a fluid, but were carried into it from the surroundings, usually on particles of dust or droplets of water floating in the air. So, gradually, it became generally accepted that bacteria, like other forms of life, arise only by multiplication from parent forms, and that sinco the germs are widespread in nature and are exceedingly small in size they are easily spread from place to place, for example, by men’s hands or in dust and water droplets in the air- Herein is a lesson for the dairyman of to-day. If he keeps in mind the small size of bacteria and the fact that they are to lie found everywhere about him, he xvill realise the necessity for Hie extreme cleanliness which is constantly being preached to all milk producers. Growth of Bacteria. Each germ is a silicic small cell consisting of a sort of jelly which wc know as protoplasm. So far as we can determine at present the germ has no

organs such as are present in higher plants and animals; but associated xvitn the protoplasm are some very active juices similer in all respects to the digestive juices of the human body. By means of these Juices the bacteria are enabled to utilise the food which exists in the liquid surrounding themSome of Hie juices split up the chemical compounds to .simple substances; others build up the simple substances into more protoplasm so that Uni germs grow in size. The changes which we observe in a substance like milk are due to the action of these digestive juices produced by the bacteria and the most marked changes are really due to the accumulation of waste products for which the bacteria have no further use. The acid which ■ultimately turns the milk sour is formed as a waste product when the bacteria use the milk sugar to get energy.

As the bacteria grow in size they begin to multiply. There are no differences of sex; each germ divides into two and the two new individuals start to grow to repeat the process. Moreover, under the most favourable conditions multiplication takes place about every half hour; so that it does not lake long for the production of enormous numbers or germs from a few originally present in a sample of milk. Herein lies part of the secret of the power of bacteria io produce extensive changes. Although each bacterium •measures on the average oniy~72Ti,ooo of an inch in length and can' produce only little change in the milk, enormous numbers all working together soon begin to produce visible ,

effects. It is a case of communal 'effort- Anything which Interferes .with ■the rapidity of growth of the germs will, of course, hamper the effort by reducing the numbers of Individual members in the community. The easiest way 'Of rendering growth more slow (apart from a shortage 'Of food) Is to lower the temperature of the •lluid in which the bacteria are living. Although cold will not kill the germs already present, It may (if Hie temperature is low enough) prevent their growth absolutely. In practice, since most bacteria thrive best at blood heat (98 degrees F.), any temperature below this leads to a slowing of the growth rate.

Bacteria and the Dairyman

There are, of course, many different kinds of bacteria; and in dairy worn some are, so to speak, friends, and some, enemies. Without the friendly types cheese would not ripen properly, butler would probably lack flavour. The enemy types, on the other hand, arc the root cause of various troubles in manufacture and bad flavours. Unfortunately, the man on the farm lias no means of telling which types are getting into his milk when he is not quite as careful as he should he. Usually, some of belli types get ih. Pasteurisation at the dairy factory destroys sonic of the germs but neve? all of them. Moreover, some of the waste products formed by the germs in Ihe milk may have spoiled it permanently before it gets in the pasteuriser. Hence, those who have to manufacture butler and cheese are anxious that the man on the farm

shall endeavour to Seep wit all types ■of bacteria, friends and enemies. The desirable friendly types can be added as pure cultures In the factory; the enemy types can never be completely eliminated when once they get into the milk.

In order to do his job properly in this matter, there are one or two points which the man on the 'farm must watch. The utensils which the milk touches must be •clean, and. if possible, all the bacteria in and on them must have been killed by heat; and, secondly, since it is never possible in practice to exclude all bacteria •the few which get into 'the milk even under clean conditions must be prevented so far as is possible from multiplying. Tills is accomplished by the process of cooling. In a word, the farmer should exclude bacteria as far as is possible and the few which get past his guard should be severely discouraged by an effleiont cooling process.