278 CIRCULATION OF THE BLOOD. 



putation experiments, the heart stops for two reasons: first, 

 because the ventricle is separated from the motor centre ; and, 

 secondly, because, by the pressure or mechanical irritation of 

 the ligature or blunt scissors, the vagus ganglion is excited. 

 In electrical excitation, on the other hand, the second of these 

 effects is produced without the first ; consequently, when under 

 the influence of atropin. the vagus ganglion is paralyzed the 

 influence of ligature and amputation, in so far as they are de- 

 pendent on severance of the sinus from the rest of the heart, 

 are unaltered, but electrical excitation is without result. 



On this subject the student will do well to consult the ori- 

 ginal papers, the references to which are as follows : As regards 

 the anatomy of the ganglia, the most important paper is that 

 of Bidder, in Miiller's Archiv, 1852, p. 163; as regards their 

 functions, Stannius (Miiller's Archiv, 1852, p. 85), Nawrocki 

 (Dcr Stanniusche Ilerzversuch, Heidenhain's Studien, 1861, p. 

 110), and Schmiedeberg (Untersuch. liber einige Giftwirkungen 

 am Froschherzen. Lud wig's Arbeiten, 1871, p. 41). 



71. Study of the Influence of Changes of Tempe- 

 rature on the Heart. (a) In the Frog. Inasmuch as the 

 influence of temperature is obviously dependent on the in- 

 trinsic nervous system, the present is the proper time for con- 

 sidering it. The modes of investigation are the same as those 

 already described in the section on endocardiac pressure. Ex- 

 act and extended researches have been made by both of the 

 methods there given, the first having been employed by Cyon, 

 the second by Blasius. Of the two, the latter is preferable, on 

 account of the greater case with which the work done can be 

 measured. The general result is, firstly, that the quantity of 

 mechanical work which can be done by the heart in a given 

 time increases with the temperature up to a certain point 

 (about 20 C., but it differs in difl'erent animals, and no doubt 

 also at different seasons), so that it may be doubled or trebled 

 by a gradual rise from ordinary winter temperature to that of 

 summer; and, secondly, that under the same circumstances 

 the frequenc} 7 of the contractions increases in much greater 

 proportion than the mechanical effect. Hence it results that, 

 although the total quantity of work done in a given time is 

 A 88 at lower temperatures than at higher, the effect of each in- 

 dividual contraction is much greater. 



If it is desired merelj r to observe the effect of changes of 

 temperature on the frequency of the pulse, much simpler ap- 

 paratus will answer the purpose. Either the whole heart may 

 be used or a part of it. In the former case, the organ having 

 been removed from the body is suspended by a thread attached 

 to the aorta in the interior of a tolerably wide test-tube fur- 

 nished with a cork, through the centre of which the thread is 

 drawn. At the bottom of the tube there is a bit of blotting- 



