348 ANIMAL HEAT. 



preference is given to the galvanometer of Sir William Thorn - 

 son. In both of these instruments the deviation of the needle 

 has a definite relation to the intensity of the current, the inten- 

 sities of any two currents being proportionate to the tangents 

 of the angles of the deviation they produce; so that, so long 

 as the same junctions are used, if the deviation produced by 

 any known difference of temperature has been ascertained em- 

 pirically, the values of other readings can be deduced from it.] 

 120. Distribution of Temperature in the Body. The 

 principal purpose to which the thermo-electrical method is 

 applied in physiology, is that of measuring the differences of 

 temperature which exist between different parts of the body. 

 These differences vary according to the proximity to, or dis- 

 tance from, the surface of the point where the measurement is 

 made, and according to the supply of blood which the adjacent 

 tissues or organs receive. Taking as a standard of comparison 

 the temperature of blood in the aorta, the facts hitherto ascer- 

 tained as to the temperature of other parts are as follows: 



1. The blood of the inferior vena cava is warmer, that of the 

 superior, colder ; but in the former this is true only of the 

 upper part of the vein just as it passes through the diaphragm. 



2. The temperature of the skin and subcutaneous tissue is 

 always considerably lower than that of the aorta, but varies a 

 good deal. 



3. The temperature of the lungs also varies. Near the dia- 

 phragm it is higher than that of the aortic blood, but elsewhere, 

 and particularly near the costal surfaces, it is lower. 



4. All the abdominal organs have a higher temperature than 

 that of the aortic blood, those in the upper part of the abdomi- 

 nal cavity being the warmest. 



5. The blood contained in the right ventricle is somewhat 

 warmer than that in the left, the difference varying from 1 C. 

 to 3 C. This difference is not dependent on the cooling of the 

 blood as it passes through the lungs ; for it is just as marked 

 when an animal is made to breathe warmed air saturated with 

 moisture. Moreover, such an hypothesis is rendered untenable, 

 by the fact that the lungs themselves are scarcely cooler than 

 the blood in the aorta. Its real cause is, doubtless, that the 

 wall of the right ventricle is in contact with the diaphragm and 

 abdominal organs, while the left is surrounded by lung. 



The recent introduction of thermometers of extreme sensi- 

 tiveness and accuracy has rendered the method less important 

 to the physiologist than it seemed to be a few years ago. This 

 may be illustrated by the remarkable fact, that the long con- 

 troversy as to .the relative temperature of the two sides of the 

 heart has been at last set at rest, not electrically, but by the 

 thermometer. 



