THE AGRICULTURAL JOURNAL. 



451 



in this regard ; whereas I always failed to 

 produce the disease by ingestion when I 

 used less than 200 ccm. 



These facts, compared with the general 

 observations, will explain why rivers and 

 other damp places are dangerous ; it does 

 not, however, bear out the general idea 

 that dew is the carrier of the morbid 

 cause, because it is impossible to under- 

 stand, firstly, how the virus can come 

 there at all, resisting sun and heat ; and, 

 secondly, in such enormous large quanti- 

 ties as are necessary to make up a suffi- 

 ciently mortal dose when taken through 

 the animal's mouth. 



To explain how the disease is taken by 

 an animal, and how it is disseminated, we 

 have to form a theory. Experiments 

 have not gone so far yet as to prove it. 

 The fact that it only needs a very small 

 quantity to infect a horse through the 

 skin on the one hand, and the compara- 

 tively large quantity which is necessary 

 to infect a horse through the mouth on 

 the other hand, point out that natural in- 

 fection very likely will go through 

 the skin. But how ? Very possibly 

 through the bite or puncture of some 

 blood-sucking insec*', as it is the case, for 

 example, in the Tsetse disease, so clearly 

 explained by the classical work of 

 Colonel Bruce, R.A.M.C. The acceptation 

 of the blood-sucking insect theory explains 

 everything with regard to dissemination 

 of horsesickness. It explains why the 

 disease is in certain low-lying parts of 

 the country, and not in the heights, but 

 that it can go there ; that it disappears 

 from one place, and comes back again. 

 The same is the case with the tsetse fly. 

 We understand now why horsesickness is 

 arrested, and finally dies out with the 

 first frosts. Seeing that the ice box does 

 not kill the viruleucy of the blood, we 

 know, by daily experience, how the cold 

 kills all sorts of flies and insects. Our 

 supposed insect flies very likely only 

 during certain times, and under special 

 conditions. From Zoological history, we 

 find that some insects appear only at 

 stated periods of the year, and during 

 certain times of the day. One year the 

 insects may be much more prevalent than 

 another, according to more favourable 

 conditions necessary to their growth, like 

 the mosquito, for instance. So we can 

 understand why the disease is rather 



scarce in stable-kept horses, and how a 

 horse which never comes oatsi le, and is 

 always fed on dried forage, is still liable 

 to contract the disease. 



We also can explain why horsesickness 

 is only in one particular season of the 

 year, although virus in a wet state is 

 virulent for at least fourteen months. 



Now it must be understood that I do 

 not think that every individual of this 

 particular insect does carry the disease, 

 neither that every bite of an insect, carry- 

 ing disease, produces it. Very much de- 

 pends on the disposition of the horse, and 

 very likely from the number of the bites 

 an exposed horse receives. For the one 

 horse one single bite may be sufficient, 

 another one may withstand hundreds. 



I cannot yet form an idea how the virus 

 is getting, in the first instance, into the 

 insect, although, in a later state, simple 

 inoculation from one animal to another 

 by the insect is possible. The fact that 

 virus, in a wet state, keeps considerably 

 over a year, and the fact that most blood- 

 sucking insects, like mosquitoes, breed in 

 damp, moist places, point to some connec- 

 tion between the two. 



I wish to point out that I do not bi-ing 

 any new theory with regai-d to these 

 blood-sucking insects as carriers of a 

 disease. They have been proved to be 

 the disseminators of human malaria, and 

 the mosquito, especially, depends in its de- 

 velopment and dissemination very much 

 from the same conditions as are known 

 in South Africa ta produce hoi-sesickness. 



The evidence brought forward to ex- 

 plain all about horsesickness has ceriainly 

 everything izi favour of the blood-sucking 

 insect. Moreover, it upholds all effectual 

 means known as a preventive against the 

 disease, and suggests, better than any 

 other theory, new ways of successful 

 treatment where a horse, necessarily, has 

 to be exposed to the infection. This 

 would be the protection of the skin by 

 covering it in some way or another, or as 

 it is done against gadflies in other 

 countries, by rubbing or smearing such 

 insecticide or strong smelling stuff on the 

 skin. The right one will have to be 

 found. There are, as it is well known, 

 many medicines in favour as preventives. 

 Their effectiveness might also find an ex- 

 planation in the above way. As the 

 whole is given as a theory, based on ex- 



