CHAPTER VI.. Disturbance in the Milk Secretion and Changes in the Milk.

DISTURBANCE IN THE MILK SECRETION AND CHANGES IN THE MILK.

Changes in the milk are so common and play so important a part in the milk industry that it is absolutely necessary to mention the more important, the country veterinary surgeon being frequently consulted on this point.

The udder acts as a natural emunctory, just like the kidney, by which are eliminated, in consequence of special selective properties, certain natural principles (the active principles contained in the forage and other food, vegetable alkaloids, etc.), drugs (alcohol), and poisons (nicotine). This physiological peculiarity explains the influence of changes of diet on the composition of the milk in mothers and on the condition of their offspring. In the human species it also explains congenital alcoholism in children, and a number of diseases whose cause was formerly unknown.

=Agalaxia.=—This term implies a temporary or definite arrest of the milk secretion. In many instances it represents nothing more than a disturbance in the physiological function of the gland, but in others it forms a true diseased condition.

Thus it is beyond dispute that psychical influences may produce disturbance in this respect. Temporary suspension in the secretion as a consequence of removal of the offspring from its mother, especially when the young animal has been sucking for several days or weeks, is a fact very well known to all breeders.

Under ordinary circumstances, however, the reasons are quite different, and when the secretion of milk is diminished or suppressed it is due to the ingestion of plants, substances, or drugs which check the secretion of milk. All the solanaceæ (belladonna, hyoscyamus, stramonium, woody nightshade, etc.), certain umbelliferæ (hemlock), colchicum, etc., have this effect.

As to agalaxia of a true pathological character, it occurs in debilitating and grave diseases, and sometimes follows certain contagious forms of mammitis complicated with sclerosis of the udder (infectious agalaxia of goats).

=Diagnosis.= The diagnosis of agalaxia presents no difficulty.

=Prognosis.= The prognosis varies, according to the determining cause. In cases of accident and in temporary agalaxia, it is sufficient to change the food in order to restore the secretion. Cooked food and warm drinks, with an allowance of roots such as turnips or mangolds, have excellent results. Where restoration of the secretion is delayed the use of what are called galactogogues has been recommended, comprising fennel, carraway, cummin, aniseed, juniper, sulphur, etc., mixed in equal parts and given in doses of 6 to 8 drachms per day for a cow.

They act principally through the stimulating effects of their aromatic principles.

MICROBIC CHANGES IN MILK.

LACTIC FERMENTS.

Microbic changes in milk are much commoner than changes of a chemical nature. Milch animals differ very markedly one from another, and, according to circumstances, give milk of ordinary composition, milk of a very rich character, or watery milk; but the most important changes in composition are those due to microbic agents.

During the milking, and according to whether this is performed in a low, dirty byre, in a clean, roomy byre, or in the open air, various numbers of germs obtain entrance to the milking vessels, and develop there with extraordinary rapidity. The milk may even become infected by non-pathogenic germs while still within the udder, in the sinus and galactophorous canals. The cleanliness of the milking vessels also has a considerable influence on the number and variety of the microbes which may eventually germinate in the liquid.

Among the microorganisms usually found in milk there are some, however, which always preponderate and play the part of organised ferments, viz., the lactic ferments and the organisms which cause coagulation of the casein; these may be regarded as normal constituents. The others are more or less foreign, and may cause important changes in the milk or cream.

The lactic ferments are numerous, comprising the lactic bacilli of Hueppe and Grotenfeld, the micrococci of Hueppe and Marpmann, and the bacilli and micrococci of Freudenreich. These different agents act on the lactose of the milk, decomposing it into carbonic and lactic acids, which coagulate the milk.

Another group of microorganisms which were well studied by Duclaux comprises those acting on the casein, among others Tyrothrix tenuis, filiformis, turgidus, scaber, virgula, etc.

These organisms secrete principles having similar effects to those of rennet, and are capable of coagulating enormous quantities of milk. After a certain time, they also secrete a second diastase, viz., casease, which acts in the ripening of cheese.

=Clotted Milk.=—This term is used in dairies to indicate milk which coagulates in lumps immediately after being withdrawn from the udder, or which coagulates spontaneously a few hours later.

The change may be of a chemical nature, depending on conditions of keep or feeding. More frequently, however, it is related to a latent non-pathogenic infection of the udder, or to immediate infection of the milk after removal by lactic ferments contained in the milk vessels or the atmosphere.

It is necessary, according to circumstances, either to modify the diet or disinfect the milk vessels, and immediately pasteurise the milk.

=Milk without Butter.=—Less commonly the diseased condition is indicated by marked diminution in the quantity of cream.

Churning only produces a poor kind of butter, particles of which do not readily cohere. This peculiarity is due to the presence of microorganisms, which have not yet been fully identified. It can be prevented by disinfection of the milking vessels, as well as of the dairy itself, and by the use of centrifugal separators.

=Putrid Milk.=—This milk is characterised by its odour. It cannot be used for making butter. In fact, as soon as the cream separates, little bubbles of gas form at various points and break, leaving small cavities. These little separate cavities reunite very rapidly, and the cream becomes reabsorbed as fast as it is formed. Afterwards oily drops formed of butyric, capric, and caprylic acids appear in the depressions and give the milk a repulsive odour (rancidity).

This change is seen during mammitis, but most commonly results from uncleanliness in byres and dairies. In the latter case putrefaction occurs about twenty-four hours after milking, and is due to the growth in the milk of Bacterium termo, lineola, etc. These organisms are present in the dust which falls into the milking pails in the byre; when milk so contaminated is stored in the dairy the changes occur.

Putrid odour may also be due to the presence of ammoniacal gas in the byre, or to special toxins liberated by microbes which have found their way into the milk. It is most marked during the warm seasons of the year.

The occurrence of putrid milk can be prevented by disinfecting the dairy and the milking pails daily for a certain time.

=Mucous, viscous, or thready Milk.=—These terms are applied to a condition which usually appears twenty-four or thirty-six hours after the milk has been withdrawn. The milk seems thick and viscous, and can be drawn out into threads like mucus. It sticks to neighbouring objects, and adheres to milk vessels like molasses. It coagulates imperfectly on standing, gives little cream, and even this cream only furnishes a mawkish, ill-flavoured butter.

In certain parts of Switzerland the production of mucous milk is favoured, because it is employed in making cheeses.

The change is due to the presence of various microorganisms. Those which have been best studied are Schmidt-Mülheim’s micrococci, the Actinobacter polymorphus of Duclaux, the Bacillus lactis pituitosi of Löffler, the Bacillus lactis of Adametz, the Streptococcus hollandicus, and, finally, three others which are much commoner, Guillebeau’s bacillus, the Micrococcus Freudenreichii, and the Bacterium Hessii. These microorganisms act on the lactose, decomposing it and causing the formation of a kind of filamentous mucilage, which can be isolated by the addition of alcohol.

The mucilaginous change in milk can be prevented by ordinary methods of disinfection.

=Red Milk.=—Milk which becomes red some hours after withdrawal, or within forty-eight hours after milking, should be distinguished from milk which on withdrawal from the udder is tinted red in consequence of hæmorrhage within the udder itself. When the milk is of a hæmorrhagic tint the blood corpuscles are soon deposited on the bottom of the vessel if the milk is allowed to remain undisturbed.

The tint which the milk assumes is due to the growth of chromogenic organisms, the best known of which are as follows:—1. B. prodigiosus, which produces large red patches on the surface. It grows readily on potato and gelatine, which it liquefies. 2. The Sarcina rosea, which develops first of all in the cream and afterwards invades the milk. It grows in sterilised milk, on alkaline potato, and on gelatine. 3. The Bacterium lactis erythrogenes, which liquefies gelatine and produces a reddish coloration. Casein can be precipitated and peptonised by means of its cultures. It develops in the milk below the cream, the serum alone becoming red, and only when shaded from the light.

=Blue Milk.=—In this case the milk appears normal when withdrawn, but some days afterwards shows blue patches, which gradually increase in size, and by uniting produce a distinct blue tint at the surface.

This change is connected with the presence of the B. cyanogenus. The organism grows in sterilised milk, but in this case merely produces greyish patches, the blue tint only occurring when a certain quantity of lactic acid is added or when the ordinary lactic ferments are present.

=Yellow Milk.=—A yellow tint occurs in ordinary milk and cream, particularly in certain breeding districts—in Normandy, for example, where the butter produced is greatly valued on account of this appearance. Pathological yellow milk is the result of the growth of B. synxanthus Schröter, which secretes a substance resembling rennet, curdles the milk, and finally dissolves the clot, at the same time producing the yellow colour.

=Bitter Milk.=—Milk which is of a normal character on being withdrawn from the udder may acquire a bitter taste some hours later. At rest, this milk produces a small quantity of yellowish, frothy cream. The organisms which produce the change have been studied in Germany, Switzerland, and Auvergne. We may mention Weizmann’s bacillus of bitter milk, Conn’s micrococcus of bitter milk, and Duclaux’s Tyrothrix geniculatus.

=Medicated Milk.=—Medicated milk may be divided into two kinds: Firstly, medicated milk proper, which differs from normal milk inasmuch as it contains a certain proportion of drugs, which, when swallowed by milch cows are partly eliminated through the udder. When taken by a young animal or child such milk has a distinct therapeutic effect, depending on the principles employed.

It does not appear, however, that up to the present any very great success has followed this system. It is possible to increase the richness of the milk in phosphates, but as regards mercurial or iodine preparations the failure has been complete.

Secondly, fermented milks, which in addition to their nutritive action are made more digestible.

Fermented milk is easily digested, and is better borne by the weakest stomachs.

In human practice the fermented forms of milk are two, viz., kephyr and koumiss.

Kephyr is prepared in Afghanistan and Persia from camel’s milk, but for some years past it has been made in England with cow’s milk. A certain quantity of cow’s milk is placed in a bottle and the ferment, consisting of kephyr grains, is added. The lactose is converted into carbonic acid and alcohol in consequence of the action of certain lactic microbes.

This milk after ingestion does not require to be coagulated and then digested before absorption, a fact which considerably diminishes peptic digestion.

Koumiss is a milk preparation resembling kephyr; it is made by the Kirghizes with mare’s milk according to the same principles, but the ferment employed gives more alcohol.

=Preservation of Milk.=—On account of the importance of preserving milk for use in large towns, in hospitals, and in the army during war, the question of its preservation has long been studied.

Chemical Processes.—The principle of preserving milk by chemical action consists in preventing, or at least retarding, the changes which inevitably follow exposure to the air. For this purpose, chemical substitutes are added which in themselves have no injurious action. Those most commonly employed are:—

Carbonate of soda 45 grs. per quart. Bicarbonate of soda 45 grs. „ Boric acid 15 to 30 grs. „ Salicylic acid 12 grs. „ Borax 60 grs. „ Lime 20 grs. „

The results obtained are of comparatively little value; the milk only keeps for a few hours, or at the most for three or four days.

Cold.—Refrigeration, which is so valuable in preserving all kinds of animal products for long periods, has also been used for preserving milk. Unfortunately, although cold impedes the development of bacteria, it also has the grave inconvenience of causing the cream to separate from the milk, and it being impossible to mix them again satisfactorily, milk preserved in this way is more or less unfit for consumption.

Heat.—The principle of preserving milk by heat is based on the destruction of the microorganisms at a high temperature. In this respect again, one meets with obstacles, for, if the heat be applied direct, some of the principles of the milk are converted into caramel, and if the temperature rises beyond 157° Fahr. (70° C.) the composition of the milk is changed.

Preservation by Oxygen.—Within the last few years the use of oxygen at a pressure of about two atmospheres has been recommended. When the milk is to be used it is only necessary slightly to relieve the pressure and allow the oxygen to escape, the liquor which remains having all the characters and qualities of fresh milk. The method appears excellent, but is too costly for every-day use.

Pasteurisation.—The pasteurisation of milk aims at destroying the greater proportion of the ferments above mentioned. The milk is heated at atmospheric pressure, and is kept for a time at a temperature of between 150° and 157° Fahr. (65° and 70° C.). It preserves its properties and composition, but sterilisation is not complete, and the milk cannot be kept indefinitely.

Concentrated Milk.—Concentrated milk is obtained by prolonged heating to 157° Fahr. (70° C.) in a vacuum, when it becomes syrupy by evaporation and its composition is not greatly modified. It is then drawn off into bottles, which are hermetically sealed and subjected to a higher temperature to complete the destruction of all the germs. Condensed milk keeps for a very long time. To prepare it for use it is mixed with a certain quantity of water, and then yields a liquid similar to normal milk.

Sterilisation.—Sterilisation necessitates the use of special apparatus in which the milk is heated in a water or steam bath sheltered from the action of the air, the temperature rising to 212° to 240° Fahr. (100° to 115° C.); all the ferments are destroyed, and the milk will keep indefinitely, but its composition is slightly modified.

=Diseases Transmissible to Man through the Medium of Milk.=—Tuberculosis.—The history of tuberculosis contains numerous facts proving the possibility of contagion by milk from cows suffering from tuberculous mammitis, though it seems necessary that the milk should be taken for a certain time to produce these effects.

Foot-and-Mouth Disease.—Observations recorded by veterinary surgeons prove that this disease affects the teats. It may be transmitted to man. The milker may be directly inoculated, but the milk is the ordinary vehicle of contagion. Chauveau saw an epidemic in a school at Lyons where milk was obtained from cows suffering from foot-and-mouth disease. In a similar way 205 persons were inoculated at Dover in 1884, and suffered from vesicles about the mouth.

Although foot-and-mouth disease is extremely benign in men, it is well to take every precaution against it.

Gastro-Intestinal Infections.—Cases have been recorded of gastro-intestinal infection in young animals and children in consequence of consuming milk which had undergone abnormal changes. Milk containing various kinds of microorganisms may at first produce lactic indigestion and afterwards diarrhœic enteritis.