PRACTICAL PHYSIOLOGY 



6l 



carefully, and, passing a thread under the sinus, 

 tighten it round the sino-auricular junction, which 

 is marked by a whitish line (x in Fig. 43). The 

 sinus continues to beat as before, but the auricle 

 and ventricle come to a standstill in diastole, con- 

 tracting, however, each time they are stimulated, 

 whether electrically or mechanically (prick). Now 

 tie a second ligature round the auriculo-ventricu- 

 lar junction. The ventricle usually gives a few 

 beats, and then again comes to a permanent stand- 



Olfactory lobes. 



Cerebral hemispheres. 

 Thalamus with pineal gland. 

 Optic lobes. 

 -VTI lU_ Cerebellum. 



Medulla oblongata. 

 Spinal cord. 



FIG. 42. BRAIN OF FROG in Situ, EXPOSED BY REMOVING THE ROOF OF THE CRANIUM. 



still. It can, however, be made to beat by artificial 

 stimulation (prick, electric shock), and the curve 

 which is obtained, if it be recorded in the same way 

 as the record of an ordinary muscle twitch (i.e., by 

 attaching the ventricle-apex by means of a hook 

 and thread to a lever, as in Fig. 44), is similar to 

 the latter except that all parts of the curve, includ- 

 ing the period of latent stimulation, are much pro- 

 longed. 



The following points can be made out in the Stan- 

 nius' preparation, viz.: (i) Any excitation of cardiac 

 muscle which is adequate to produce a contraction 



