234 ANIMAL PHYSIOLOGY. 
also follow from the intercostal muscles being simply unsup- 
ported when the heart recedes. 
INVESTIGATION OF THE HEART-BEAT FROM WITHIN. 
By the use of apparatus introduced within the heart of the 
mammal and reporting those changes susceptible of graphic 
record, certain tracings have been obtained about the details of 
Fic. 209.—Marey’s cardiac sound which may be used to explore the chambers of the heart. 
(after Foster). a, is made of rubber stretched over a wire framework, with metallic 
supports above and below ; 3, is a long tube. 
which there are uncertainty and disagreement, though they 
seem to establish the nature of the main features of the cardiac 
beat clearly enough. An interpretation of such tracings in the 
Il. 
b . | 
/'\ 
| tp a | nad Lal LL” \ 
al rT eee | 
P| Right auricle. 
é| |, 
| sal 
, 
i 2 / 
Alen | |---| | Right ventricle. 
eee | ens 
qa’ 
¢ A 
b N ; 
Lv Kes V\_/ |Cardiac inpulse. 
aT a 4 | 
NL 7 | | i 
Fia. 210.—Simultaneous tracings from the interior of the right auricle, from the interior of the 
right ventricle, and of the cardiac impulse, in the horse (after Chauveau and Marey). 
Tracings to be read from left to right, and the references above are in the order from top 
to bottom. A complete cardiac cycle is included between the thick vertical lines I and Il. 
The thin vertical lines indicate tenths of asecond. The gradual rise of pressure within the 
ventricle (middle tracing) during diastole, the sudden rise with the systole, its maintenance 
with oscillations for an appreciable time, its sudden fall, etc., are all well shown. There is 
disagreement as to the exact meaning of the minor curves in the larger ones. 
light of our general and special knowledge warrants the fol- 
lowing statement. 
