§ 5.112 RESPIRATION 185 



as in moulting; it can be induced artificially by chilling the brain. 

 Injection of extracts of prothoracic gland can also break diapause. 

 Even if D is the cause of diapause here, it is still not known whether 

 the action of the prothoracic hormone in bringing diapause to an 

 end is to inhibit the further secretion of D, or to release the tissues 

 from its action, as in the adult Bomhyx. 



The fact that the diapause of hosts and their parasites is normally 

 synchronous provides further evidence that diapause is determined 

 hormonally (Hinton, 1957). For instance, an ichneumon, Diplazon 

 fissoriuSy parasitizes several species of syrphids, although some of 

 them diapause and others do not. If an active parasite is trans- 

 planted (Schneider, 1950) from an active host to one that is 

 diapausing, the parasite becomes immobile ; but in the reciprocal 

 case, when the diapausing parasite is transplanted from a dia- 

 pausing larval host to an active pupal host, the parasite resumes 

 active growth. It therefore seems that the hormones of the host 

 are able, not only to control the metabolic level of its own tissues, 

 but also to override those of the parasite. 



Vertebrata. There is not much conclusive evidence for hor- 

 mones that decrease oxygen consumption in vertebrates, except 

 in amphibians and possibly mammals. 



Amphibia. A significant decrease in oxygen consumption, of 

 about 30 per cent, occurs in starved frogs in the 4th and 5th weeks 

 of treatment with A.C.E., an extract of the adrenal cortex, if 

 0-36 ml/Kg body weight is injected on alternate days (Calhoon 

 and Angerer, 1955). There is no difference in loss of body weight 

 during this period as between injected frogs and untreated 

 controls. The authors do not specify which cortical steroid is 

 dominant in Upjohn's extract which they used. It might be 

 expected that one of those concerned with carbohydrate metabol- 

 ism, rather than one of the ''mineralocorticoids", would decrease 

 oxygen consumption. 



Mammalia. Decrease of basal metabolic rate and of oxygen 

 consumption occurs chiefly in hibernating mammals; at other 

 times the possible need for a hormone having this action would 

 seem to be confined to maintaining the normal equilibrium in 

 opposition to the thyroid (§ 5.111). There has been much work 

 on the effect of injecting extracts of adrenal cortex into mammals; 



