46 PROCEEDINGS OF THE COTTESWOLD CLUB 



muscular fibres. The l)ir(l tribe have a high degree of 

 respiration and a low irritability ; the reptiles have a high 

 degree of irritability and a low degree of respiration. 

 This law holds good not only in the different genera of 

 animals, but also in the different stages or states of the 

 same animal under altered conditions. The structural 

 changes of an animal from one condition to another, or 

 from one stage to another, are always a change from a 

 lower to a higher degree of respiration, and from a higher 

 to a lower degree of irritability. Thus the changes from 

 the egg to the bird, or from the tadpole to the batrachian, 

 or from the larva to the insect condition, are changes in 

 which the quantity of respiration is augmented, and the 

 degree of irritabilitv is diminished, whilst on the other 

 hand, the physiological changes in the degree of activity 

 in animals, [for example, during sleep] but especially in 

 that remarkable condition which is called hibernation, the 

 rcsjjiration is diminished, whilst the degree of irritability 

 is augmentetl. 



On what this susce[)til)ility of change de[)ends, and 

 ('S[)ecially on what the power of taking on an augmented 

 irritability depends, is at present unknown. But 1 think 

 that in this power we may find one clue to the secret of 

 hibernation. I take it for granted that all animals have 

 the power, or privilege, of slee[)ing. During sleep, 

 resj)iration is in its intervals diminishetl only as a rule 

 slightly ; the irrilal)ility is j)robably proj)ortionately 

 increased, and this may be one object of the [)eriod of 

 rei)Ose. So it is that after a night's rest we wake up and 

 feel invigorated for the day's work. So also if we do not 

 sleep, or sleep only fitfullv, we do not feel ourselves 

 as fully " fit " as we should like in the morning. This 

 l)henomenon has its limits, and limits beyond which it 

 cannot })ass, so far as we are concerned. But in some 

 animals the boundary line is beyond ours; their limit 

 beyond ours. In them the quantity of respiration is still 



