08 



THE AGBI G U LTU BAL JOURNAL. 



sickness is microbic in nature, or due^ to 

 the agency of a micro-organism which 

 has hitherto eluded discovery. This con- 

 clusion seems warranted when we con- 

 sider the well defined period of incuba- 

 tion, sudden accession of urgent symp- 

 toms, and the certainty of infection by 

 means of the injection of a minute dose 

 of virulent matter. 



The fact that we are not able to demon- 

 strate the organism does not negative the 

 possibility of the agency of such in the 

 production of the disease for we have 

 several parallels in liacteriology such as 

 rabies, small-pox, etc., etc., in which we 

 are equally unsuccessful in our search for 

 a causal microbe. Possibly improved 

 optical apparatus may bring these minute 

 bacteria within our sense of sight, but it 

 is more probable, seeing the great effici- 

 ency to which lenses are brought in 

 modern years, that we shall have to fall 

 back upon corrobatory evidence by the 

 existence of a specific organism such as 

 may be furnished in the investigation of 

 this disease. 



(rt) Subcutaneous or traumatic theory. 

 — The argiaments in favour of this mode 

 of infection are numerous and weighty, 

 pointing to the agency of insects rather 

 than to simple traumatisms or v.'ounds 

 being the points of ingress of the disease. 

 These later must be very varying both 

 as to place and manner, and the fact 

 exists that no connection has been traced 

 l)etween cases of severe traumatism or 

 wound and instances of the disease (such 

 as obtains in the disease Tetanus). 



The only argument tending to confirm 

 the simple traumatic theory seems to be 

 the prevalence of cases as reported by 

 some observers immediately after the 

 early frosts and before the weather has 

 become so cold at night as to be inhibitive 

 to bacterial life. In this case it has been 

 suggested that the act of feeding on frosted 

 pasture being followed by an increase in 

 the number of cases might indicate that 

 the cause usually lay in some laceration 

 of the tongue or lips and the introduction 

 of the disease consequently through these 

 channels of the mouth and tongue, a.id 

 the incidence of cases about this time 

 might 1)0 held to be related to such a 

 cause, and indicate a possible clue to the 

 manner of general infection. 



The fact that animals receiving cut and 

 carefully gathered food, in whom no such 

 lesions presumably exist, suffer from the 

 disease, and also that the disease attains 

 its maximum violence at periods free from 

 frost, would tend to discount such a theory. 

 Such a cause in any case could only be 

 operable in a very small percentage of 

 cases of the disease, and its significance is 

 accordingly not great. 



The Insect Theory.— li the agency of 

 insects as disease-carriers is admitted, no 

 fact which has occurred to me in con- 

 sidering horse-sickness exists to exclude 

 the possibility of the principle being 

 applied in this disease. Presumptive 

 evidence— where all theories are at pre- 

 sent presumptive or tentative — points to 

 the possibility of such an agency in the 

 case of the malady in question. 



The points tending to confirm such an 

 hypothesis are many, and parallels are not 

 wanting in the case of such diseases as 

 the malarial fevers of man, filiariasis of 

 the blood of man, both due to the well 

 proved agency of the mosquito. Yellow 

 fever, proved recently to be due to infec- 

 tion by the mosquito, elephantiasis, 

 malaria of sparrows, bats, etc. (furnishing 

 an instance of the infection of the lower 

 animals by the mosquito) the pyrosomal 

 disease (red-water) due to the tick, and 

 Ngana or Tsetse-fly disease, and the 

 various instances brought forward from 

 time to time of the spread of disorders by 

 the puncture of fleas, bugs, all instancing 

 the power of insects to produce disease in 

 and transfer the disease from man to man, 

 some probably only mechanically _ as 

 intermediary bearers without alteration 

 of life cycle, and others as definitive 

 hosts in which the specific organism 

 undergoes a phase of development in the 

 body of the insect before it is capable of 

 becoming infectious to man. 



In consideration of this heading the 

 weight of evidence in the production of 

 horse-sickness seems to be in favour of 

 inoculation by the puncture of some 

 insect whose habits closely conform^ to 

 those of the culicidoe or mosquito family. 

 Arguments in favour of this theory are 

 reconcilable with the existing ideas, ex- 

 periences, and folklore of those having a 

 practical experience of the disease for 

 many years. 



