UNANESTHKTIZED POIK[LOTHERMIC DOG— KELLER 63 



ex])osure ; there was no shivering. This straiglit h'ne fall in core temperatnre at the 

 rate of 3.^° C. j^er hour with no change in slope that might indicate the retention 

 (if reniiianta] ri'gulatiir\- ])n\vers has heen the criterimi used for characterizing the 

 completely poikilothermic animal. \\ hen the preparations were removed from the 

 3° to a 22° C. amhient temperature, core temperatures remained stationary at 28° C. 



The tissue defect in each of these preparations was a reasonal)ly selective thermo- 

 coagulation of the i)osterior half of the hypothalamic gray. Sagittal sections taken 

 from the series on Dog 2S are shown in figure 2 and illustrate the location and extent 

 of the tissue defect which rendered this animal completely ])oikilothermic against 

 cold. Observe the sharpness of the edges of the lesion with no distortion of adja- 

 cent tissue and the absence of debris or scar in the defect — it has simply become a 

 part of the third ventricle. It has been our experience that a lesion which eliminates 

 all regulation against cold does not leave any gray caudal or lateral to the lesion but 

 in turn the defect need not involve the tissue lying immediately adjacent to this 

 gray. If posterior hypothalamic gray remains, a proportional ability to combat cold 

 also remains ; it matters n(jt whether the intact gray be situated laterally, medially, 

 dorsally or ventrally. If a relatively large portion of the posterior hypothalamic 

 gray remains undisturbed, the animal's regulation against cold does not deviate 

 materially from the normal. 



The partially poikilothermic animal. Cooling curves demonstrating retention 

 of remnantal cold combatting powers are graphed in figure 3. A curve which has 

 been interpreted as indicating the absence of non-shivering heat production with 

 retained remnantal shivering heat producing ability is shown in the instance of 

 Dog 112. For the first two hours the core temperature fell at the same rate as in 

 the completely poikilothermic animal after which, at a core temperature of 31° C, 

 shivering began and sufficient heat was produced to slow body cooling materially. 

 A curve suggesting the retention of remnantal non-shivering heat producing ability 

 is shown in the instance of Dog 53. Here the core temperature fell progressively in 

 essentially a straight line but more slowly than in tire instance of a complete deficit ; 

 shivering was not in evidence at any time. A cooling curve which indicates the reten- 

 tion of both non-shivering and shivering heat producing ability in remnantal amounts 

 is shown in the instance of Dog 527. At first the core temperature fell in a straight 

 line but more slowly than in the instance of Dog 28, until it reached 32° C. at 

 which time shivering began and rapidly produced sufficient heat to prevent further 

 body cooling. 



A slower cooling rate in the absence of shivering might be due to retained ability 

 to reduce heat loss by conductance rather than to an increase in internal heat. How- 

 ever, the fact that such preparations exhibit a spontaneous rise in body temperature 

 when removed to an ambient temperature of 22° C, whereas the core temperature 

 of the completely poikilothermic dog does not, has been interpreted by us as giving 

 presumptive proof of retained non-shivering heat producing ability both in relation 

 to hypothalamic ablations and localization of nerve fiber pathways at lower levels.^- * 



Oxygen consumption determinations on such preparations have verified the cor- 

 rectness of this interpretation as illustrated below in figures 5, 6 and 7. 



