A STUDY IN MO UP, ID AND NORMAL P(IVSIOLO(;Y 53 



reserve, because we cannot rely upon the working of tlie calorimeter at a liigli 

 temperature as accurate. 



The conclusions reached, if correct, would indicate that after section of the 

 cord there are two distinct antagonistic forces at work, the one depressing, the 

 other increasing, the production of animal heat. As has already been stated, section 

 of the spinal cord causes vaso-motor paralysis, to which is believed to be due in 

 great part if not altogether the thermic changes in the animal economy which fol- 

 low the operation. It is of course entirely possible that the tliermic changes may 

 be the result of some unknown influences. This could be definitely settled if we 

 had the power to isolate the action of the vaso-motor system by dividing the cord in 

 such a way as to leave intact the vaso-motor nerves whilst severing all other fibres. 

 Since this cannot be done, the question naturally suggests itself: is it possible to 

 cut the spinal cord above the vaso-motor centres; and if this be possible, what is 

 the eflect of such division upon the thermic functions of the body] The answering 

 of these questions comes so imperatively into the present inquiry that it is neces- 

 sary to step aside for a time from what might be considered the direct line of 

 investigation. 



The usual test for the integrity of the vaso-motor system is tlie effect of the gal- 

 vanization of a sensitive nerve upon the blood pressure after the animal has been 

 quieted with woorara and the pneumogastrics severed. Under these circumstances 

 normally there is a very great rise of arterial pressure, and if this fail to occur 

 vaso-motor paralysis is known to exist. 



Dr. C. Dittmar [Benchfc ilhcr die VerJianiUunr/en der Koni(jL SacJi.i. Gescllscliaft 

 der Wissenschaften vac Leipzig. Math. Phijs. Glassc. 1870, Bd. xxii.) is the first 

 experimenter to whose original paper I have had access, who proved that, after 

 separation of the medulla from tlie pons, irritation of a sensitive nerve still causes 

 a great increase of the arterial pressure. Thus in his experiment a (p. 33) on a 

 rabbit, the medulla having been previously cut at its junction with the pons, the 

 pressure rose 29 millimetres of mercury in 16 seconds, and in experiment />, both 

 peduncles of the crura cerebri having been previously divided, tlie rise amounted 

 to 30 millimetres. 



I. Owsjannikow (Beriehte, etc., Bd. xxiii.) has experimented very elaborately, 

 and has found that in cats and rabbits the dominant vaso-motor centre is in a 

 region whose upper boundary is one or two millimetres below the corpora quadri- 

 semina, and whose lower boundary is four to five millimetres above the point of 

 the calamus scriptorius. 



Owsjannikow divided the nerve centres with very fine knives, and employed the 

 effect upon the arterial pressure of galvanizing a sensitive nerve as a test of the 

 integrity of the vaso-motor centre. His experiments have every appearance of 

 care and accuracy. 



K. Heidenhain (PfUiger's Archiv, 1871, Bd. iv. p. 55-2) has also, in numerous 

 experiments, determined that separation of the medulla from the pons in dogs does 

 not prevent tlie rise of arterial pressure when a sensitive nerve is irritated. 



The results obtained separately by Dittmar, Owsjannikow, and Heidenhain, are 



