196 
Theory and Practice of Dipping 
obtained in the laboratory. Attention was first called to this infertility 
of the eggs of dipped females by Lounsbury (1905). 
Brlinnich and Smith (1914) concluded from experimental observations 
that the poison is in part absorbed through the skin of the tick subse¬ 
quent to the time of dipping and is also imbibed with the fluid extracted 
from the skin of the host. 
According to our own experiments with dipped animals, an effective 
dip kills the ticks before they can lay eggs, and this even applies to 
ticks removed from a host which has been subjected to periodical 
dipping. This is an important point when considered in relation to the 
results obtained by Ransom and Gray bill, which showed that simple 
immersion of free adult ticks taken from an undipped host failed to 
kill. 
Watkins-Pitchford (1911a), in his observations on the effect of the 
dip on adult female ticks attached to the host, writes (p. 69) as follows: 
‘How rarely after one dipping such female forms remain on 
their host uninjured, and go on to full distension, may be judged 
from the fact that out of over 10,000 adult ticks actually counted 
throughout these observations on cattle being subjected to the 
new process, only sixty-nine partially distended females have been 
found. 
‘Careful detachment of these distended ticks and observations 
under favourable conditions show that—in the majority of cases— 
the dipping arrests the process of egg-laying, while of those eggs 
which are laid only a small percentage are capable of subsequently 
hatching out.’ 
Again (p. 50): 
‘It. can be shown that the poisonous effect, though strictly 
local, is not due to a simple deposition on the surface of the skin, 
resulting from one or more dippings. If, in an habituated animal, 
a patch of skin is shaved closely and then thoroughly washed so 
as to remove all deposited arsenic with the hair and surface epi¬ 
thelium before attaching the ticks, the lethal result will follow in 
the same degree as in the case of an habituated animal in which 
such precautions have not been taken.’ 
Watkins-Pitchford also found that ticks w^ere killed wdren placed on 
an animal after dipping; and, further, that this effect persisted for 
several days (see Appendix I). Similar experiments carried out by us 
have given the same result. 
