70 KINETIC HORMONES — I 



Vertebrata. There are no specific hormones in vertebrates to 

 control somatic muscles, although these are noticeably affected by 

 the hormones from the gonads and also to some extent by thyroxine 

 and adrenaline. For instance, the loss of testosterone in castrated 

 mammals, such as cart-horses, results in lowered spontaneous 

 activity and muscle tone, and is shown by the whole stance of the 

 animals, as compared with a stallion, Equus. In females, the pres- 

 ence of oestrogen in the circulation during oestrus (§ 4.234 and 

 Part II, § 4) is accompanied by a great increase in activity, as has 

 been shown by attaching a pedometer to a sow. Similar variations 

 in activity are shown during the 4-day oestrus cycle of rats (Beach, 

 1948) ; a loss of 82 per cent in muscular activity can follow ovari- 

 ectomy. It seems probable that all these effects and those of thyrox- 

 ine may be the result of metabolic changes caused by changes of 

 hormone balance, rather than of any direct kinetic action of the 

 hormones on the muscle contractions, or even on the tonus. 



The action of adrenaline is slightly to prolong the active state of 

 the muscle fibres and to increase the tension accompanying a 

 twitch initiated by the nervous system; it does not itself cause 

 contraction of skeletal muscle as it does in the case of visceral 

 muscle (Goffart and Ritchie, 1952). 



3.2 Control of pigmentary effectors 



Pigmentary effectors of a variety of animals bring about colour 

 changes mainly in two distinct ways: one in which extrinsic 

 muscle fibres change the shape of the colour-containing cells, and 

 the other in which the pigment granules themselves are moved 

 within the confines of a stationary cell. Rarely, the cells change 

 shape and may even move their position. These processes cause 

 so-called physiological colour changes (Tables 8 and 9). "Morpho- 

 logical colour change" (Sumner, 1940, and Dawes, 1941) produces 

 similar effects by slow alteration in the total amount of pigment 

 present, rather than by its redistribution. This reinforces the 

 adaptive physiological changes when the external conditions 

 remain relatively constant for days or weeks. Together they play 

 an important part in providing "protective coloration" for the 

 animal. 



