PHYSIOLOGY. 



661 



tcrnal temperature in the same manner as a 

 cold-blooded animal ; that toward the end of in- 

 cubation, about the twentieth or twenty-first 

 day, there is an intermediate stage in which no 

 marked response is observed ; and that this ap- 

 parently neutral condition is succeeded, when 

 the chick is hatched, by a stage in which it reacts 

 as a cold-blooded animal. The apparently neu- 

 tral stage may be the resultant of 2 opposite 

 tendencies on the one hand, the cold-blooded 

 condition ; on the other hand, the imperfectly 

 developed power of regulating the production of 

 heat. This interpretation seems to be supported 

 by the experiments that show that the interme- 

 m'ediate stage may give way to the cold-blooded 

 or to the warm-blooded condition, according as 

 the chick is feeble or strong and healthy. It 

 appears that the power of regulating the pro- 

 duction of heat depends upon the integrity and 

 full development of the nervous control of mus- 

 cular action. The healthy chick, when exposed 

 to cold, responds by active muscular movement 

 and increases its production of heat and carbonic 

 acid ; in the case of the feeble chick, the cold 

 may produce not increased excitability but col- 

 lapse, when the chick is unable to respond by 

 increased muscular activity, and passes into a 

 condition resembling that of a cold-blooded 

 animal. 



The experiments of M. S. Pembrey on the re- 

 action of animals to changes of external tem- 

 perature turned upon the production of heat as 

 determined by the amount of carbonic acid dis- 

 charged from the animal. In the mouse the out- 

 put of carbonic acid was rapidly increased as the 

 temperature was lowered, and concurrently with 

 the increase the animal's muscular activity be- 

 came more vigorous. In the developing chick 

 the effect of the cold on the twenty-first day was 

 to decrease the discharge of carbonic acid, the 

 chick in this stage behaving like a cold-blooded 

 animal. A comparatively sudden change took 

 place from this day on-ward, and the chick acted 

 like a warm-blooded animal. Newly hatched 

 pigeons reacted for the first few days like cold- 

 blooded animals, the output of carbonic acid de- 

 creasing with the fall in external temperature. 

 The influence of muscular activity upon the 

 production of heat was further shown by details 

 of observations made upon mice after section 

 of the spinal cord and during anassthesia; in 

 both cases the 'muscular paralysis was accom- 

 panied by a change in the reaction, which now 

 resembled that of a cold-blooded animal. 



Experiments by Loewy indicate that the in- 

 terchange of gases in respiration remains com- 

 paratively unaltered, notwithstanding great va- 

 riations in the composition of the surrounding 

 air. Pressure, even doubling the amount of 

 oxygen, rarefaction of the air, and great diminu- 

 tion in the amount of oxygen seem to exert but 

 little influence on the elimination of carbonic- 

 acid gas or on the absorption of oxygen. 



The effect upon respiration of exciting the 

 cerebrum in a nonana?sthetized animal is prob- 

 ably a complex one. yet, as is shown by W. S. 

 Spencer, by careful regulation of the anaesthetic 

 state four constant effects can be obtained upon 

 respiration by stimulation of the cortex, and 

 these can be traced down each in a course of its 

 own from the cortex to the medulla oblongata. 



Slowing and arrest of the respiratory rhythm 

 was obtained in the cortical area situated just 

 outside the olfactory tract, in front of the point 

 where the tract joins the temporosphenoidal lobe. 

 On exposing successive and vertical sections of 

 the hemisphere the same result was obtained by 

 excitation applied in the line of the strand of 

 fibers known as the olfactory limb of the an- 

 terior commissure. After decussating at the 

 anterior commissure, the tract is continued back- 

 ward on either side of the infundibulum into 

 the red nucleus below and external to the aque- 

 duct at the plane of exit of the third nerve. 

 The other three effects are in the form of in- 

 creased action. The first of them is accelera- 

 tion, which may be followed, beginning from a 

 point on the coiive*x surface of the cortex within 

 the " sensori-motor " area, back just below the 

 lenticular nucleus, where it borders on the outer 

 and ventral portion of the internal capsule. 

 The strand runs at first external and then ven- 

 tral to the motor portion of the internal capsule, 

 and so reaches the tegmentum. The lines from 

 the two sides meet at the level of and just be- 

 hind the exit of the third nerve. The second 

 effect, of hyperinspiratory clonus, or " snuffing 

 movements," was obtained by excitation at the 

 junction of the olfactory bulb and tract, and then 

 carrying the stimulation backward along the ol- 

 factory tract ; the same result was found when 

 the uncinate convolution of the temporosphe- 

 noidal lobe was irritated. Followed from the 

 uncus this excitable region passed behind the 

 optic tract to the crus, arid then lay ventrally to 

 the crusta. The excitable tract on each side thus 

 converged toward the middle line at the upper 

 border of the pons. The other experimental re- 

 sult of hyperinspiratory clonus is of such fre- 

 quency and constancy as to be clearly an impor- 

 tant general phenomenon. It can be elicited in 

 various ways ; for example, excitation of the de- 

 scending motor tract in the cornus radiata and 

 internal capsule yielded this result ; so did exci- 

 tation of the fifth nerve and dura mater, as well 

 as of the sciatic nerve, both before and after 

 complete removal of the cerebrum. 



From their experiments, made to determine 

 the influence of bleeding and transfusion upon 

 the respiratory exchange, M. S. Pembrey and 

 A. Gurber find that severe bleeding, whether 

 followed by transfusion or not, causes no decrease 

 in the respiratory exchange, provided that the 

 animal's nutrition does not suffer from the 

 operation. The respiratory quotient shows vari- 

 ations, but these are apparently not greater than 

 those observed in the normal' animal. The ef- 

 fect of the bleeding is marked by the animal's 

 diminished reserve store of energy. Although 

 the loss of blood does not prevent the so-called 

 vegetative processes from going on, yet the ani- 

 mal is unable to undergo any great muscular 

 exertion, such as would be easily borne by it 

 in the normal condition. The respiratory ex- 

 change is not regulated by the red corpuscles, 

 the carriers of oxygen, but by the demands of 

 the tissues. The animal, when it is at rest, is 

 able to accommodate itself, even to a loss of one 

 half of its haemoglobin, and the exchange of 

 material represented by respiration is as great 

 as that of a normal animal when it also is at 

 rest ; the cells are able to obtain an adequate 



