40 



i-i; V i;k. 



iiiti-rior and cMtiim I'l if ir^'aiiism. li is (•crtaiii that tlio normal unirnal lias 

 soino inctluxl of fontrollinj^ tlu- loss of bodily heat, at K-ast within certain limilu. 

 Modification of the unionnt of perspiration is in man very inHuential, but in the 

 do-j, the general surface ha\ injj no perspiratory jjlands, this factor sinks into in- 

 hi'Miificjince. The only metluxis which are at the control of the do-jj for re{;ulatin{» 

 heat loss are throiif^h the respiration anil through the external circuhition. Thus 

 when heat is to be retaini-d, a i)artially cooled layer is maintained between the 

 inner hot binly and the external cold air by shutting off in a measure- the circulation 

 from the superficial parts. On the other hand, when the superficial capillaries arc 

 dilated, the heated surface rapidly gives up its caloric. After section of the cord, 

 the superficial capillaries cannot be contracted, and as a natural result, the animal, 

 so far as concerns heat dissipation, is purely dependent upon its environment, and 

 an increased loss of heat must occur in a cool atmosphere. Lowered bodily tem- 

 perature, with increased loss of heat, is the usual and normal result of a section 

 of the cord practised low enough down to cause a wide-spread vaso-niotor palsy. 

 In the Spitz dog (Experiment 32) this increased loss did not occur, probably 

 because the extraordinary protection of the body by the very thick outer coat 

 interfered with surface cooling. The extremely minute quantity of heat dissipated 

 by the liairy S[)itz has already been indicated. In Experiment 33 there was no 

 decided increase in loss of heat because the cord was cut so low down that a very 

 insignificant portion of the vaso-motor system was affected. 



The immediate effects of section of the cord upon the loss of heat having been 

 determined, it seems natural to inquire whether there also is an increased heat pro- 

 duction following the operaticm. Before entering upon this investigation, however, 

 it is well to determine; whether tlie increased dissipation of lieat be j)ersistent, or 

 whether it occur only in the few hours iuunediatcly following section. It is plain, 

 if the increased loss of heat be permanent, there must be an increased production aa 

 well as an increased dissipation of caloric. At first the heat stored up in the l»ody 

 may be drawn upon, but this source of sup[)ly is of course soon exhausted, and any 

 increased dispersion then means increas(>d production of heat. The converse of 

 this, however, does not of necessity follow, for it is possible to have a primary 

 increase with a later decrease of production. Thus it is chemically very conceiv- 

 able, that merely lowered temperature can check tissue change, i.e., prochiction of 

 caloric. It is well known that external heat, by raising the internal temperature, 

 is capable of causing fever, with its excessive metamorphosis of tissue: and it would 

 seem probable that cold clu-cks chemical movements inside as well as outside of 

 the body. The liistorv' of hibernating animals is a case in point; in them, with 

 lowered temp«'rature there is lowered chi-mical activity. 



The next experiments were therefore directed to deciding wluther the increased 

 dissii.atii>ii of heat, after section i<f tli.' i md, is persistent or la>ts only a few hours. 



