400 INSECTS AND SOME DISEASES OF STOCK 
at different stages. A knowledge of the length of time any 
particular stage remains on an animal is imperative, otherwise 
the dipping-fluid may be applied at such an interval that the 
tick had been on the animal, conveyed, or taken infection, and 
left before the next application. 
The blue-tick, which passes all stages on the one host, and 
stays there about a month, is naturally more easily dealt with 
than the brown-tick, which in its dangerous larval and nymphal 
stages may only remain on an animal for as short a period as 
three days, and a dipping-bath efficacious against the first 
would be practically useless against the second. 
The time various stages of tick remain on the ground is 
equally important. They do not live for ever ; and it has been 
shown that by destocking pastures for eighteen months all 
Ixodidae will have been starved out. This is not always 
possible ; but destocking of portions of the land may also be 
employed. Suppose, for instance, an owner has several cases 
of East Coast fever in cattle grazing on a portion of his land. 
If he so kraals those animals that the infective larvae or 
nymphae fall on a restricted area, he may with confidence move 
the clean balance of his herd to the uninfected lands. These 
larvae and nymphs will take at least a month to moult and 
become infective, by which time the stock has been moved out 
of their range. 
Such are the methods for circumvention of disease, which 
are only possible when full knowledge of parasite and insect 
has been acquired. The study is as yet in its infancy ; but 
even this infant has effected savings of millions of pounds. 
How much more will the grown-up be capable of ? 
To reach the grown-up stage quickly there must be more 
workers following upon organised lines. If I have set your 
cerebral cells moving in this direction and obtained one disciple 
to the view that my subject is natural history in the real 
meaning of the term, I am satisfied ; for I know this Society 
will foster that disciple, and one can reasonably look to the 
day when it will have achieved even greater celebrity as an 
organisation competent, qualified, and willing to consider the 
vast economic problems which lie even within the least of the 
lesser animals. 
