RELATIVE VIABILITY IN MAMMALS AND BIRDS. 469 



is to say, there is no case where the maximum duration is near 

 what might be expected, and the average duration bears a 

 reasonable relation to the maximum. Individual exceptions, or 

 knowledge from other sources, show us the ages to which animals 

 may attain ; the records show the complete failure to get near 

 what is possible. Where comparative experiments have been 

 made the contrast is amazing. Compare the large cats, which 

 were relatively well housed, with the small cats, which were 

 confined in an overheated house without access to open air ; 

 compare the civets, which were kept out of doors, with the genets 

 and paradoxures, kept in a heated house ; the larger canines with 

 the smaller forms ; the ratels and badgers (unheated) with other 

 mustelines (heated) ; the raccoons (unheated) with coatis (heated); 

 the squirrels and porcupines (unheated) with most of the other 

 rodents (heated) ; the larger marsupials and wombats (unheated) 

 with the smaller marsupials (heated). 



The most fatal type of housing for any mammal (or bird) is 

 being confined to the interior of a warmed house, without free 

 access to the open air. The conditions of course are very 

 complex, and I do not suggest that the provision of heat is in 

 itself an evil. The ideal throughout the period I am discussing, 

 and which still maintains an evil existence in the minds of a 

 majoi-ity of those who have to do with living animals, is that, in 

 the first place, animals have to be kept warm. Warmth having 

 been secured, the more advanced persons have consented to, or 

 even urged, the advantage of ventilation, moistening of the air, 

 and so foi-th. The idea, however, is wrong. The first requisite 

 is free access to the open air, the next is light, space and clean- 

 liness ; these things having been secured, any form of heating 

 that may be thoug-ht advisa,ble, may be added in so far as it does 

 not in any loay interfere loith the 2}rimary considerations. So far 

 as I can judge from my experience and observations, the main- 

 tenance of an equable temperature, and p]:-obably even a gi'eater 

 amount of heat than is usually provided, is important in the case 

 of reptiles and of young or sick mammals or birds. Adult 

 mammals and birds, if in a normal state of health and if provided 

 with tolerable space for exercise, not only do not require an 

 equable temperature, but thrive better if they are subjected to 

 changes of temperature. The best possible conditions for them 

 are free access to large open-air enclosures, with adequate wind- 

 screens, and with the possibility of retreat to small, dry shelters, 

 which may or may not be provided with some form of artificial 

 heat. The smaller such shelters are the better, and certainly they 

 should not be, whether heated or unheated, part of a building to 

 which visitors have access. In a much larger number of cases 

 than is generally supposed, if such shelters are small and dry, and 

 provided with appropiiate bedding, artificial heat is unnecessary. 



Mammals and birds, if they have room for exercise in fresh air, 

 not only can maintain the heat of their bodies, but as a dii-ect 

 reaction to the stimulation of air and change of temperature, 



Proc. Zool. Soc— 1911. No. XXXI. 31 



