PRACTICAL CONDUCT OF EXERCISE XVIII 153 



that this is not actually the case ; and though their severance is easily carried out and for 

 research results is advisable, this slight addition to the operative procedure has been omitted 

 since the student has a good deal to get through in the time available. Severance of the 

 muscles attached to the great trochanter of femur has also been omitted and severance of upper 

 end of the rectus femoris (a small muscle in the cat) for similar reasons as not actually 

 necessary, though of course advisable if the observations are conducted for research. 



The speed of movement of the travelling recording-surface should not be less than 

 20 cm. a sec. With the larger Palmer student-drum this means one revolution in 5", 

 with the smaller (ordinary size) drum one revolution in 2'5". The manipulation for the 

 exercise is therefore easier with the larger drum. The recording-lever of the myograph is 

 preferably one with a screw ' after-load ' support. The resistance offered by the myograph 

 is preferably a spring and not a weight. A coiled letter-weight spring is lighter and more 

 durable than rubber tube or band, and takes less room. 



In some patterns of recording-drum the drum is carried on the rotating spindle by 

 a spring catch, and when the drum stops or starts quickly it is liable to 'lag' or 'rush' on 

 the spindle, upsetting the time-relations of the records and rendering the marking of the 

 latencies erroneous. For this experiment the drum must be clamped to the spindle firmly 

 so as to retain a fixed position on it. 



Good material for the writing-point of the myograph-lever is oil tracing-paper : this 

 has sufficient spring in it, and the spring is not affected by moisture. 



III. V. The drill with its drill-heads is of ordinary pattern, quite inexpensive, and 

 purchasable at any hardware shop. It serves also for the next-following exercise, XIX. 



EXERCISE XIX 



Decerebrate rigidity {Jnl. of Physiol, vol. xxii, p. 319, 1898) is essential for the first 

 part of this exercise, which makes use of it in the vastocrureus for the examination of postural 

 reflexes and as a background against which to exhibit the reflex inhibition of that 

 muscle. The rigidity rapidly ensues on decerebration and appears much before the ether- 

 chloroform narcosis employed during the performance of the actual decerebration has passed 

 off or even greatly diminished. The grade of rigidity establishing itself varies somewhat ; 

 for this exercise the grade does not matter much, even a small degree sufficing for the 

 observation. It is well to remember that the degree of rigidity at the knee (vastocrureus) 

 is greater in the supine position of the preparation than in the lateral position (Magnus and 

 de Klejn, Arch. /. d. ges. Physiol, cxlv. 455, 1912). Occasionally the rigidity after setting 

 in wanes and may disappear ; this may result from haemorrhage from the brain-stump into 

 the posterior cranial fossa, behind tentorium cerebelli ; removal of the blood or checking 

 of further haemorrhage will then restore the rigidity. 



In the exercise severance of the rectus femoris muscle as a precaution against occurrence 

 of flexion at the hip is not included in the procedure. It is best done at the iliac origin of 

 the muscle ; but its omission makes no practical difference to the results of the exercise. 

 Similarly, severance of the glutei, obturator internus, gemelli, and quadratus lumborum as a 

 precaution against extension of hip in the contralateral reflex, though necessary for research 

 work, is unnecessary for the exercise and is omitted. 



