THE AGRICULTURAL JOURNAL. 



131 



Intermediary Bearer. Assuming the 

 iU'ti\c agency of the moscjuito in dis- 

 seinenating- the disease horyesicknoss, the 

 difficulty of establishing the complete 

 life-cycle of the organism, and the 

 identity of the hypothetical intermediary 

 bearer remains, unless the casual organ- 

 isjn IS always simply transterred Irom 



one equine subject to another. It is 

 impossible to altogether exclude the 

 view that perhaps a parallel may exist 

 between the Malaria of man and this 

 disease of the horse, which furnishes 

 several points of analogy. The difficulty 

 of establishing the life history of the 

 malarial organism, and the manner in 

 which mankind becomes its victims have 

 been very great, yet in the case of malaria 

 it was at least possible to demonstrate 

 without difficulty the organism after it 

 had once gained an entry into man's sys- 

 tt iii, the chief dithculty being in showing 

 that it depended solely upon the mos- 

 qnito for its development and pro})aga- 

 tion. _ The maxim of "iSTo mostpiito, no 

 malaria," is already passing into a truism. 



In horsesickness, however, \\-e have not 

 the advantage of being able to demons- 

 trate a large organism more or less lilling 

 the blood corpuscle and develo[)i]io- with- 

 in it, but we have, as 1 have said above, 

 to take it for granted that a microbe is 

 concerned in the production of this dis- 

 ease, and, working upon that assumption, 

 we have to endeavour to trace its life 

 history unaided by the eye. 



It has been noticed for years that 

 mules partially, and donkeys almost en- 

 tirejy, enjoy a high degree of immunity 

 to attack, as well as much insusceptibility 

 to artificial infection. The possibility of 

 their acting as harbourers of the organism 

 without in themselves manifesting physio- 

 logical disturbance must not be lost sight 

 of, somewhat in the way that we believe 

 the large game of the ' Tsetse-fly belts 

 harbour the organism of 'Ngana, or as 

 the acclimatised ox will, while apparently 

 healthy, act as a host to a modified form 

 of the red-water organism (Pyrosoma 

 Bigeminum), and l)e capable of re-estab- 

 lisbing the disease in its acute form in a 

 susceptible animal, or, again, as the 

 native child in a malarial district is the 



host and the means by which the malaria 

 of man is propagated and maintained. 



Such a theory would not conliict with 

 the possibility ol direct transference from 

 one acutely infected animal to another, 

 \\ hich, in the presence of an active agent, 

 such as the mosquito, might develop into 

 an epizootic of magnitude, or what we 

 should call a '"wave of the disease." 



It is possible, again, that cases which 

 have recovered from the disease (so- 

 called salted animals), may assume the 



role of host, and furnish infective 

 material for the propagation of the dis- 

 ease. That this is improbable, however, 

 seems likel}' from a consideration of the 

 well established fact that the immunity 

 conferred by an attack of the disease is 

 of so short duration and frail character 

 as to lead one to doubt in many cases if 

 recovery {•nurciv iiiiiuuiiity at all. 



Sc\eral .li^linrt allueks may be pro- 

 Hiiced in the same animal at sliort in- 

 tervals, antl this with so little diminu- 

 tion in intensity that the disease may 

 prove fatal after an animal has success- 

 fully resisted three, or possibly four, pre- 

 vious well-marked artificially induced 

 attacks. The theory that such an animal 

 should, during the intervals of those at- 

 tacks, be harbouring the organism in a 

 modified form seems unlikely, as in such 

 an instance re-infeetion could probably 

 only occur from a distinct and acute case 

 of the disease. 



It seems more probable, therefore, that 

 the organism exists in a modified form 

 ni some insusceptible intermediary host 

 if the agency of the mosquito in the pro- 

 duction of the disease is to be proved to 

 be a correct surmise. Such intermediary 

 host, however, need not necessarily be an 

 insusceptible equine or even a warm 

 blooded animal at all, for wo know that 

 frogs, for instance, are capable of 

 harbouring in their systems forms of 

 parasitic life not dis-similar to the 

 malarial organism, while they are in- 

 separable, of course, from the moist and 

 marshy localitief we are led hy our ex- 

 perience to look upon as so closely con- 

 nected with tlie disease in question. 



{To he continued.) 



