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XXI] infected by placing in his mouth the clinical thermometer used by his son recently invalided from Malta on account of the disease. It is now known that the infection is conveyed in milk, and it has been suggested that it may be introduced in other kinds of food, or in water. Water as a usual medium may be dismissed, but there is strong evidence, judging from naval and military opinion, that, though the usual, milk is not the only medium. Facts point very distinctly to goat's milk as the most important medium of infection. The micrococcus is present in the milk of 10 per cent, of Maltese goats. Monkeys are easily infected by feeding them on such milk. Immediately on the goat's milk supply to the naval and military hospitals in Malta being stopped the cases of locally acquired undulant fever practically ceased. Formerly this fever was very common in Gibraltar. The milk supply of the garrison at that time was largely from goats imported from Malta. Gradually these goats have died out or been got rid of, and no more Maltese goats have been imported. Concurrently with this there has been a marked and proportional reduction of undulant fever cases in the garrison. In 1905 the s.s. Joshua Nicholson shipped 65 goats in Malta. An epidemic of undulant fever broke out on board, nearly all those who drank the milk of the goats being attacked. IMMUNITY.— Bruce holds that one attack confers immunity from subsequent attacks; other authorities believe that one attack, so far from conferring immunity, actually predisposes to subsequent attacks. The latter is Bassett-Smith's opinion, based on the fact that he finds the bactericidal power of the serum and the phagocytic energy of the leucocytes lowered during, and for some considerable time after, an attack of the disease.

iNCUBATION period.— The period of incubation in the naturally acquired disease is difficult to fix.Cases have occurred as early as six days after arrival in Malta; others as late as fourteen and seventeen days after the subject of it has quitted Malta. Some have held that it may remain latent for months.