PHYSIOLOGICAL 263 



the wind-shaken environment of the herbage. A reflex that brings 

 about immobility may be very profitable in such circumstances, 

 for when an animal keeps perfectly still it is less likely to be pounced 

 upon by enemies, many of which will not look at booty that does 

 not move. And although among higher animals there is an interesting 

 automatic adjustment of the falling body, so that it "falls on its 

 feet", it is probably on the whole advantageous not to be very 

 energetic when there is an accident. 



Many insects, like the black dung-beetle, the death-watch, the 

 ant-lion larva, and the stick-insects, show a ready assumption of 

 the cataleptic or "death-feigning" immobility, which is at any 

 rate closely analogous to animal hypnosis. It is enough to take the 

 water-bug Ranatra brusquely out of the pond to see it become as 

 stiff as a dry twig. A fall, a good shaking (as in children!), a slight 

 pressure, a nip, a sudden blaze of light, and so on, may serve to 

 induce cramp-immobility. Many experiments have been made with 

 the common stick-insect (Dixippus morosus), which moves cautiously 

 about at night, but remains motionless and twig-like by day. By 

 letting the quaint creature fall twice or thrice, and in other ways, 

 it is easy to induce the so-called cataleptic state; and the way in 

 which the arms of a human cataleptic can be bent and fixed in a 

 peculiar position is readily mimicked in Dixippus. The insect will 

 remain standing on its head for an hour, yet it is enough to breathe 

 on the creature to bring it back to normal life. It may be mentioned 

 that the cataleptic state in this type is not assumed unless the brain 

 is quite uninjured. The stick- insect is so immobile in its catalepsy 

 that it can be stretched like a bridge between two books lying on 

 the table, and then it may even be weighted in the middle with 

 paper-clips! We believe that this insect holds the record for the 

 duration of its immobility, which may last for four and a half hours. 



There are doubtless different grades of animal h)rpnosis; thus 

 there must be a long inclined plane between a hypnosed suckling 

 pig that cannot move, yet follows us about with its eyes, and the 

 catalepsy of a stick-insect, or between the death-feigning of a 

 spider and the "stiff-cramp" of a brittle-star. What is common to 

 all cases is, first of all, some abrupt change that "shocks" the 

 nervous system, and sometimes prevents the normal answer being 

 given to an excitation. This may be followed, in experimental cases 

 at least, by an increased intensity of muscular effort, which is not 

 allowed to become effective. In the second place, whether the phase 

 of intensified effort be passed through or not, there is a marked 

 change in the normal tonus of the muscles. When muscles are not 

 being contracted in the ordinary way, associated with moving 

 about or doing external or internal work, they are in a state of 

 tonus. This means, if we may treat a difficult subject lightly, that 

 they are in a st9.te of slight permanent contraction, in obeciienc^ 



