2oO Journal of the Department of Agriculture. 



developed toxin production, thus indicatiEg that infection could hv 

 transmitted over some consideial)le intervening space. 



In regard to Onderstepoort a low degree of natural infection 

 does, however, exist, since in more than one case last summer a local 

 carcass developed a toxicity which could not he traced to foreign 

 infection. Whether this low natural infection is a permanent feature 

 of the area, or wliether it is merely maintained on the Onderstepoort 

 farm hy the constant introduction of animals from the outside, is not 

 yet clear. In any case it does not matter much, since there is 

 practically no pica on the farm, and therefore no danger of the stock 

 jicquiring natural lamziekte. 



In regard to the natural distril)ulion of the causal organism 

 throughout the country very little can be said as yet. We know that 

 there are areas in which the organism is present, but in which no lam- 

 ziekte occurs because pica is absent ; and we know that there are 

 extensive areas in which pica occurs but from which the organism 

 appears to be absent, and which are therefore free from lamziekte; 

 but that is all. 



In regard to the scattering of infection, four common modes may 

 be reg'arded as important- — blow-flies for short distances, and dust, 

 birds, and moving animals, for longer distances. 



When examining a carcass undergoing decom])ositi()]i during the 

 warmer parts of the year, the presence of blow-iiy larvae in enormous 

 numbers is noted, and these larvae undoubtedly assist in the rapid 

 putrefaction of the cadaver. They are themselves toxic, and although 

 generally left untouched by pica animals, they, can produce the disease 

 experimentally when drenched in sufficient amount. The pupae from 

 such larvae are also toxic, and the causal organisms can be obtained 

 in mixed culture either from larvae or pupae. Undoubtedly the 

 blow-fly larvae help to distribiite the toxin-producing bacteria 

 throughout the carcass, especially by carrying the infection from the 

 aerobic surfaces into the anaerobic depths of the tissues; while the 

 blow-flies themselves can help to scatter infection by mechanical 

 carriage from one carcass to another. 



But in the winter months, when blow-flies are absent, carcasses 

 may still develop toxicity, and the flies are therefore by no means 

 essential to distribution. Under these conditions we must assume 

 infection from soil and dust. As already mentioned, the causal 

 organisms produce spores, and, as in the analogous cases of anthrax 

 and c{uarter-evil, such spores may remain A'iable in the soil for a 

 considerable length of time. Exactly how long an infected soil can 

 remain infected we do not know. It is an interesting- i)roblem for the 

 future to determine the interval over which a soil can harbour viable 

 spores or germinated bacteria, in competition with the normal soil 

 flora, once the favourite habitat (carcass material) is abolished. 



We have just stated that carcasses nuiy develop toxicity in the 

 winter time, but it must now be emphasized that winter decomposition 

 is not nearly so dangerous as the rajjid jjutrefaction of summer. 

 During the last winter season at Armoedsvlakte a considerable pro- 

 portion of the carcasses were found non-toxic, and of the carcasses 

 Avhich were toxic a larger quantity of debris was required to produce 

 the disease. During the cold dry weather the tendency of the carcass 

 is I'ather to mummify than to putrefy. Blow-fly ^arvae, those agents 



