92 PRACTICAL PHYSIOLOGY 



fibres consist largely of the clear variety, and the hyoglossus of 

 the granular variety, i.e. a muscle in which the majority of muscle - 

 fibres contain more nuclei and are relatively richer in undifferen- 

 tiated living material, the sarcoplasm. The chief physiological 

 differences between granular and clear muscles are, that granular 

 muscles have a slower and more prolonged contraction, are less 

 exgitable, more easily tetanised, and less readily fatigued. 



In mammals the same differences between red and white muscles 

 can be shown to exist. Red muscles, such as the masse ter or 

 soleus of the rabbit, differ structurally in having more sarcoplasm 

 and nuclei in their fibres, and are redder in colour owing to a much 

 richer capillary network between then* fibres and to the presence 

 of myohaematin in the fibres themselves ; physiologically they are 

 far less readily fatigued and show a contraction four or more times 

 as long as that of the white gastrocnemius (Fig. 95). The experi- 

 ment can be made after the rabbit has been killed by breaking its 

 neck. 



For comparison with the single twitch of the gastrocnemius, 

 that given by the hyoglossus may now be studied. This muscle, 

 arising from the anterior edge of the body of the hyoid cartilage, 

 runs forwards into the substance of the tongue. 



A Hyoglossus Preparation is made by cutting off the whole of 

 the lower jaw, including the tongue and hyoid cartilage. Place it 

 on the myograph board, mucous surface upwards, turn the tongue 

 forwards, and connect its tip to the lever by a thread. Firmly fix 

 the hyoid cartilage by running a pin through it into the cork. Two 

 needle electrodes transfix the base of the muscle just in front of 

 the hyoid. 



All the other connections are the same as when studying the 

 single contraction of the gastrocnemius ; a weight of 5 or 10 grams 

 is placed near the axis of the lever. 



Compared with the single twitch of the gastrocnemius, that given 

 by the hyoglossus (Fig. 96) shows the following differences : the 

 whole contraction lasts more than twice as long, the latent period 

 is slightly longer, but it is the period of shortening and still more 

 that of relaxation which is more gradual and prolonged. 



Action of Veratrine. A brainless frog is poisoned by injecting 

 into the dorsal lymph sac 5 minims of a saturated (1 in 1000) solu- 

 tion of veratrine in normal tap- water saline. In order that the 

 drug may be rapidly absorbed it is important not to " pith " the 

 frog, but to destroy its cerebrum with a pair of Spencer- Wells 

 pressure forceps. In about ten minutes it will be observed that 

 the hind legs are very slowly and imperfectly flexed after a jump, 

 and a few minutes later the frog will be seized by a spasm when 

 it jumps. As soon as these symptoms appear the remaining por- 

 tions of the central nervous system are destroyed, and a sciatic 

 and gastrocnemius preparation made. 



In the meantime the action of veratrine may be studied on the 



