1908] on the Extinction of Malta Fever. 21 



probability that gross contamination of the surface of the soil takes 

 place by infective discharges, rendered this view likely. 



Experiments were made to put the theory to the test. Dust was 

 artificially contaminated with micrococci and blown about a room in 

 which monkeys were confined, or blown into their nostrils or throat. 

 Several of these experiments were successful. It was therefore proved 

 that dust artificially contaminated with 7nicrococcus melitensis could 

 give rise to the disease. 



This, however, was no proof that this mode of infection occurs in 

 nature. The artificially contaminated dust contained myriads of 

 micrococci. Under natural conditions, they could seldom be numer- 

 ous, and the powerful Maltese sunlight would tend to kill them off 

 rapidly. The dust blown about by the wind must also dilute the 

 micrococci to an enormous extent, so that it is only possible to con- 

 ceive of a micrococcus here and there in a vast quantity of dust. 

 Experiments were therefore made with dust naturally contaminated, 

 in order more closely to resemble natural conditions. Dust contami- 

 nated in this way, and also that collected from suspicious places and 

 blown about the cages, sprinkled on food, or injected under the skin, 

 always gave negative results. 



The conclusion was therefore again come to that conveyance of 

 the infective germ by means of contaminated dust could only rarely, 

 if ever, give rise to the disease. 



Btj Mosquitoes or other Biting Insects. — As already mentioned, 

 the theory had been strongly advanced that Malta fever, like yellow 

 fever or plague, might be conveyed by blood-sucking insects. The 

 fact that the micrococci are frequently found in the peripheral blood, 

 gave some colour to the belief. This point was therefore fully 

 investigated and numerous experiments made with the different 

 species of mosquitoes found in Malta, and also with other blood- 

 sucking insects. 



The results, again, were all negative, and it was therefore decided 

 that Malta fever is not conveyed by contact, by contaminated dust, 

 or by mosquitoes. 



What, then, could be the mode of spread ? 



By Way of the Alimentary Canal.— li had long been known 

 that the smallest quantity of the micrococci introduced under the 

 skin or applied to a scratch would give rise to the disease in man or 

 monkeys, but some work by previous observers had led us to believe 

 that infection did not take place by way of the mouth in food or 

 drink. They had fed monkeys on milk contaminated by the micro- 

 cocci, and stated that in no case had infection taken place. This 

 observation kept the Commission at first from making feeding experi- 

 ments. As infection, however, did not appear to take place by 

 contact, by the inhalation of infected dust, or by mosquitoes, it was 

 clearly necessary to repeat these feeding experiments. 



