494 



journal of Agriculture , Victoria. [lo Aug., 191 2. 



considerably in arriving ai a correct diagnosis. Tliis culture method can 

 go on through many generations, and though the first may be some- 

 what mixed — that is to say, contain more than one distinct organism — 

 it is possible by sub-cultures to eventually obtain a perfectly pure culture 

 of the organism concerned. Microscopical examination of these cultures 

 from time to t'me will reveal the organism originally inoculated into the 

 tube. They may be also grown on plates (Fig. 9). In order to prove 

 that a micro-organism is the cause of a clisea.se, it is necessary (1) that 

 the organism in question, as recognised by its form, mode of grovvth, or 

 products, be found constantly associated with the disease at least in the 

 earlier stntres nnd in sufficient numbers to account for "he svmptnms ;. 



A. Mature female and egg^. 



B. Hide showing cattle ticks. 



C. Various stages of cattle ticks. 



(2) that pure cultivation of thi; 

 organism through sufficient gene 

 rations be made, until it ma's 

 reasonably be .supposed tha 

 everything else which couh 

 possibly have been taken fron 

 the animal that yielded thi 

 organism has disappeared . 



(3) that other susceptible anima 

 be inoculated with the culti- 

 vated organism, and that tht- 

 disea.se be reproduced ; (4) that 

 the same organism be found in 

 the tissues of the successfully inoculated animals in such numbers, 

 and with such a distribution, as to account for the disease. In 

 many cases it is necessary for the organism which produces disease 

 to be transferred from one animal to another by means of inter- 

 mittent hosts, such as biting flies, ticks, mosquitoes, fleas, &c. (Figs. 10, 11) ; 

 as an example, the disease known, at any rate by name, to nearly all, as 

 " Texas " or " Tick Fever" in cattle. This is caused by a small organism 

 — from 12,000 to 80,000 being required to measure i inch (Fig. 12) — which 

 gains access to the red blood corpuscles of the animal, and produces a 

 train of symptoms, of which fever and red water are constant. The 

 organism is carried from animal to animal by means of the tick (Fig. 13). 



Another disease, which many in the northern districts will be familiar 

 with, is tick fever in poultry (Fig. 14). The organism in these cases assumes. 



