TRANSACTIONS. OF SECTION I. 535 
which most commonly transfers the poison or liying parasite from one animal to 
another is known as the ‘ brown tick,’ Rhipicephalus appendiculatus. Koch sup- 
posed that the common ‘blue tick’ was the agent. The credit belongs to 
Dr. Lounsbury and Dr. Theiler of having shown that it is chiefly the ‘brown 
tick’ which acts as carrier; but Theiler has proved that 2. simus is also able to 
transmit the disease. Without the intervention of a tick, as far as we know at 
present, it is quite impossible that the parasite of this disease can be transferred 
from one animal to another. For example, if we take a quantity or blood con- 
taining enormous numbers of these piroplasmata, and inject it into the blood 
circulation of a healthy animal, the latter does not take the disease. In the same 
way, if cattle affected by East Coast Fever are placed among healthy cattle in a 
part of the country where nonqof these ‘ brown ticks’ are found, the disease does 
not spread. It is evident, therefore, that some metamorphosis of the parasite must 
take place in the interior of the tick, and this new form of the parasite is introduced 
by the tick into a healthy animal, and so produces the disease. In this particular 
disease the virus or infective agent is not transmitted through the egg of the tick, as 
is the case in some of these parasitic diseases, but only in the intermediate stages of 
the tick’s development ; that is to say, the larva which emerges from the egg of the 
tick is incapable of giving the disease. What happensis this. The larva creeps on to 
an infected animal and sucks some of its blood. It then drops off, les among the 
roots of the grass, and passes through its first moult. The nympha, which is the 
name given to the creature after its first moult, is capable of transferring the 
disease to a healthy animal: that is to say, if it crawls on to a healthy animal and 
sucks blood from it, it at the same time infects this healthy animal with the germ 
of E.C.F. In the same way, if a nympha sucks infected blood from a sick animal, 
it is able, after it has moulted into the adult stage or imago, again to give rise to 
the disease if placed, or if it crawls, upon a healthy animal. 
The Life-history of the Brown Tick.—I throw on the screen a slide repre- 
senting the four stages of the life-history of the brown tick: The egg, the larva, 
the nympha, and the adult or imago. The eggs are laid on the surface of the 
ground by the adult females, who deposit several thousands at a time; and 
these hatch out naturally, if the weather is warm and damp, in twenty-eight 
days. But this period of incubation of the eggs may vary very greatly owing 
to differences in temperature. Immediately after the larva is born it crawls to the 
summit of a blade of grass or grass stem, and there awaits the passage of some 
animal. If an ox passes by and grazes on the grass, the tick at once crawls on to the 
animal, and, having secured a favourable position, starts to suck the ox’s blood. It 
remains on the ox for some three or more days, when, having filled itself with 
blood, it drops off and lies among the grass. The first moult, under favourable 
conditions, takes twenty-one days, when the nympha emerges. In the same way 
the nympha crawls on to an animal and fills itself with blood. As a nympha it 
also remains on the animal for about three or four days. It again drops off into 
the grass, and at the end of eighteen days emerges from its second moult as the 
perfect adult male or fémale. The males and females again crawl on to an ox, 
where they mate. After this the female tick ingests a large quantity of blood, 
which is meant for the nourishment of the eggs, and agains drops off, sometimes 
as early as the fourth day, into the surrounding grass. After about six days she lays 
her eggs in the ground, and the cycle begins again. 
These ticks are very hardy, and in the intermediate stages can resist starva- 
tion for long periods, so that a larva or nympha or adult tick may remain 
perched at the end of a blade of grass for some months without finding an oppor- 
tunity of transferring itself to a suitable animal. On this account it comes about 
that even if all infected cattle are removed from a field the ticks in that field will 
remain capable of transferring the infection to any healthy cattle which may be 
allowed into this field for a period of about a year. At the end of a year or 
fifteen months, however, the infective ticks are all dead, and clean cattle may be 
allowed into the field without any risk. If one takes these facts into consideration 
it will be seen that a single ox may spread this disease for a distance of some 200 
wiles, if trekking through the country at the average rate of ten miles a day. For 
