May 14, 1908] 



NA TURE 



41 



secretion, or by way of the intestinal tract. Or it miglit 

 leave the body by way of the blood, by the agency of 

 mosquitoes or other biting flies. 



Many experiments were made along' all these lines, and 

 finally it was decided that this micro-organism leaves the 

 body principally in the renal secretion, and in the bloud 

 taken out of the body by blood-sucking insects. 



The result, therefore, of this experimental w-ork was 

 to give rise to the belief that the disease was either con- 

 veyed from the sick to the healthy by contact, by 

 inhalation of infected dust, or, lastly, by the agency of 

 mosquitoes. 



How DOES THE yiicrococcus melitensis gain Entrance 

 TO THE Body? 



The investigation of these various modes of infection 

 was therefore undertaken. 



By Contact. — Let me first consider infection by con- 

 tact. Experiments were made by placing monkeys, one 

 affected by Maltia fever, the other healthy, in more or less 

 :ntimate contact, and it was found that if the monlieys 

 ■ived together in the same cage infection did take place. 

 If, on the other hand, the monkeys were kept in the same 

 cage, but separated by a wire screen, so that, although 

 they could touch each other, contamination of the healthy 

 monkey's food by the sick monkey could not take place, 

 then infection did not take place. 



In regard to this question of conveyance by contact, 

 there is one argument against it which has always seemed 

 to me unanswerable, and that is that thousands of cases 

 of .Malta fever have been invalided home to England, and 

 treated in our naval and military hospitals, without, as 

 far as I am aware, a single case of the fever arising 

 among the patients, orderlies, or nursing sisters. 



It was therefore concluded that contact with Malta 

 fever patients, or the handling of infected clothing or dis- 

 -harges, is not the mode of infection. 



Then the question of infection by contaminated dust 

 was taken up. 



By Dust contaminated by the Micrococcus melitensis. — 

 For some time it was considered probable that this would 

 prove to be the common method of infection. The fact 

 that the micrococcus withstands drying for a long time, 

 the dusty nature of Malta, and the probability that gross 

 contamination of the surface of the soil talces 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 contamined with Micrococcus melitensis 

 could give rise to the disease. 



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

 occurs in \ature. The artificially-contaminated dust con- 

 tained myriads of micrococci. Under natural conditions 

 they could seldom be numerous, 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 contaminated 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 con- 

 veyance of the infective germ by means of contaminated 

 dust could only rarely, if ever, give rise to the disease. 



By Mosquitoes or other Biting Insects. — .'\s already 

 mentioned, the theory had been strongly advanced that 

 Malta fever, like yellow fever or plague, might be con- 

 veyed by blood-sucking insects. The fact that the micro- 

 cocci 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 thcre- 



NO. 20 II, VOL. 7SI 



Hod« or tnl^ltpo. 



P>T»b«b)r 



AccidantAl teediog . 



Uilk + M. ; itomftcb 

 tubo 



Duet + Mediloi 



PoUto 



BplMD 



fore 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 .ilimentary Canal. — It had long been 

 known that the smallest quantity of the micrococci intro- 

 duced under the skin or applied to a scratch would give 

 rise to the disease in 



man or monkeys, but Malta Fever 



some work by previous 

 observers had led us to 

 believe that infection 

 did not take place by 

 wav of the mouth in 

 food or drink. They 

 had fed monkeys on 

 milk contaminated by 

 the micrococci, and 

 stated that in no case 

 had infection taken 

 place. This observa- 

 tion kept the Com- 

 mission at first from 

 making feeding experi- 

 ments. As infection, 

 however, did not 

 appear to take place by 

 contact, by the inhala- 

 tion of infected dust, or 

 by mosquitoes, it was 

 clearly necessary to 

 repeat these feeding ex- 

 periments. 



Feeding Experiments. 



Here is a table show- 

 ing the result of some 

 of these feeding experi- 

 ments, and you see it is 

 abundantly proved that 

 .Malta fever can be 

 conveyed to healthy 

 animals by way of 

 the alimentary canal. 

 Even a single drink of 

 a fluid containing few 

 micrococci almost certainly gives rise to the disease 



(F'g- 4)- 



From the results, then, of all these experiments it 

 seemed most probable that the micrococcus gained an 

 entrance to the body by way of the alimentary canal, and 

 therefore bv some infected food or drink. 



Di>. 



Hilk 



Mother't milk 



Milk + OQltora 



Fig. 4.- Feeding experiments. 



Fig. 5. — Milking goat 



This led to an examination of food-stuffs, and among 

 these the milk of the goat is one of the most important. 



Infection bv Means of Go.ats' Milk. 

 The goat is very much in evidence in Malta, and sup- 

 plies practically all the milk used. There is, I believe, 

 one goat to every ten of the population, so that, as there 



