G. H. F. Nuttall 
493 
manner stood around the card, the number of lice wandering out of the circle being 
noted. After 4 experiments, at the commencement of which the positions of the 
persons and card were successively altered, we concluded that the lice wandered 
out in a purely random manner and that Crocker’s result must have been due to 
one or both of the extraneous factors already mentioned. 
Conclusions regarding repellants. 
The following considerations, in conjunction with my experiments 
above cited, may serve to explain the apparent contradictions contained 
in the foregoing statements made by different authors. (1) Certain 
substances (oils of anise, cloves, eucalyptus, naphthaline, carbolic acid, 
etc.) do exert a repellant action on lice, this being clearly demonstrated 
by experiments, conducted in the dark, wherein the insects were given 
the free choice of wandering towards or away from the substance 
tested, two pieces of cloth of like texture and size being placed side by 
side, the one being impregnated with the substance and the other not, 
the insects, at the start, being placed in the space between the two 
pieces of cloth. (2) Hungry lice placed on ordinary cloth may wander 
away from it in search of warmth and food. If a repellant is dropped 
upon such a piece of cloth the subsequent scattering of the lice from it 
may be falsely attributed to the action of the repellant alone. (3) When 
a repellant is dropped upon an infested cloth the lice frequently remain 
attached to it; they seem to prefer to face it and remain clinging to the 
cloth. (4) Tests of repellants conducted in the light do not give a fair 
measure of their effect because the instinct of the insects to flee from 
the light may overcome their desire to avoid the repellant. (5) Con¬ 
versely, hungry insects will feed upon the skin in spite of the presence 
of repellants upon it, their behaviour in this case being comparable to 
that noted under (3) where the instinct to remain clinging to cloth is 
stronger than the instinct to avoid the repellant. (6) The negative 
evidence previously cited (p. 489) can largely be explained in the light 
of this conflict of instincts on the part of the insects, the stronger 
instinct overcoming the weaker. (7) It is therefore difficult to attach 
importance to the action of so-called repellants in practice, the evidence 
indicating that hungry lice will attach themselves to man and feed 
upon him in spite of them. I believe that these substances protect man 
because they act in the main as insecticides and not as repellants.* 
(8) There is no proof that lice are more attracted to some persons than 
they are to others; where this appears to be the case it may be owing to 
a variety of extraneous factors. 
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