TO SOME DISEASES OF STOCK 
897 
buildings, under stones and other sheltered places of camping- 
grounds, and only come out to feed especially at night. A 
few minutes suffice for the meal, and they then retire to their 
seclusion to digest the meal, and in the case of the female to 
lay a few eggs. This programme may be repeated whenever 
opportunity offers, for these ticks may live for two or three 
years. 
The disease-germs wdiich these Argasidae can carry are 
of a particular genus known as Spirillum, or Spirochaeta ; and 
not only is the tick, once infected, capable of giving the disease 
at succeeding bites, but the young, born of an infected mother, 
are also infective. Spirillum or relapsing fever of man, and 
spirillum disease of fowls, are the only two conditions in this 
country caused by the Argasidae with which I am familiar. 
The second group, or Ixodidae, is that in which the popularly 
called tick falls. The adults of this group remain on an animal 
for many days, during which time blood is being ingested. 
When replete, the female drops to the ground, and under a tuft 
of grass or other shelter proceeds to lay her eggs to the number 
of several thousand, and then dies. She does not, as is the case 
with the Argasidae, return to the attack, and she is therefore 
incapable of spreading disease directly from one animal to 
another. 
From the egg a minute larva or seed-tick hatches, in one 
to two months, and these larvae climb up a blade of grass and 
there await the arrival of a passing animal, to which they attach 
themselves. In a few days they become engorged with blood, 
and, according to the species of tick, either fall to the ground 
in order to moult into a nymph, or undergo that change on 
the host’s body. 
If they fall to the ground, they seek a sheltered spot again, 
and in one to two months the emerged nymph is once more 
awaiting a passing animal. 
The nymph feeds upon the host for some days, and when 
engorged once more requires to moult — an operation which 
takes place on the animal or on the ground, depending again 
upon the species concerned. One to two months after the 
repletion of the nymph, the fully mature and sexually perfect 
adult or imago, which results from the moult, is ready to feed 
