162 
Development of Hook-worms 
1911) who discusses nearly every aspect of the subject except the 
purely medical treatment. This work is unfortunately not usually 
accessible to the general reader, but a short abstract has appeared in 
the British Medical Journal (1912). 
From the point of view of preventive medicine one of the most 
interesting and useful contributions to the subject is that of Boycott 
(1911) who summarises the results which he and Haldane obtained 
during and after the Cornwall outbreak (1902-1905). This paper also 
includes a useful comparative study of the results obtained by other 
observers. 
Since then the most important experimental work on the subject 
is that by Ffilleborn (1914). 
It is unnecessary for the present to make mention of other papers 
dealing with the matter of life-history and development. These will 
be referred to as occasion arises. 
As described in general works on Parasitology the normal life-history 
of the hook-worms is briefly as follows: 
The adult worms in the human intestine produce eggs in considerable 
numbers, more or less constantly throughout their sexual life, but 
occasionally with intermission, the reason for which is not at present 
clearly understood. From clinical observation, however, it is well 
known that infected persons may show a large number of eggs in their 
faeces every day over a long period, but on one or more days there 
may be few or practically none at all. This is a frequent source of 
trouble in determining the existence of hook-worm infection, especially 
in cases which have received inadequate treatment. 
The eggs which are produced by the adult worms are carried through 
the intestine and are voided along with the faecal matter in the ordinary 
course. These eggs are of a very small size, measuring only on an 
average 0-06 x 0-04 mm. They possess a very thin shell. Within 
this there is a thin yolk membrane which is quite transparent and 
inside this in the fresh state can be seen four approximately globular 
cells, the two larger being situated towards the poles. These cells are 
compressed against each other. Less commonly eggs with eight or 
more cells may be observed. 
If, now, this faecal material be deposited in some suitable place the 
eggs will proceed to develop. Suitable conditions are not difficult to 
find in all tropical countries and in most sub-tropical countries. They 
are met with occasionally even in regions far removed from the tropics. 
The essential conditions are heat, moisture, air and food. The first 
