288 



PHYSIOLOGY 



CHAP. 



of warm-blooded animal.- are, mi the contrary, impossible, except under 

 certain special conditions, and acquaintance with these conditions is one ot 

 the most recent acquisitions of scientific technique. 

 A. Cold-Blooded Animals. In order to obtain 

 cardiac movements in the frog or any 



other 



FK;. 121. Luciani'a tonographic apparatus for 



the beats of the heart, when isolated and attached to 

 cannula at different heights of the auricles (semi 

 schematic), c, Reservoir of serum or other nutrient 

 fluid, closed by Mariotte's method so as to keep the 

 tilling and pressure of the heart constant ; b, valvular 

 apparatus, closed during systole ; <; tap for interrupting 

 communication between the reservoir and the heart ; d, 

 cannula to which the heart is tied, fixed to appara- 

 tus ; e, small vessel full of serum, which can be raised 

 during the experiment, so as to bathe the whole of the 

 outside of the heart ; /, small mercury manometer, pro- 

 vided with float, which records the beats of the heart on 

 the revolving cylinder with a glass pen. 



graphic tracings of the 

 cold-blooded animal, three 

 different methods may be em- 

 ployed. Of these there are 

 various forms, the most im- 

 portant being : 



(a) Tonographic Methods. - 

 These consist essentially in 

 the use of a small mercury 

 manometer, which records 

 the oscillations of the internal 

 pressure of the, frog's heart in 

 relation to the phases of its 

 activity. The apparatus re- 

 presented by Fig. 121 fulfils 

 all requirements for studying 

 the mode in which the activity 

 of the heart exhausts itself, 

 when excised from the animal, 

 filled with a nutrient fluid, 

 and exposed to constant dia- 

 stolic pressure at a given 

 temperature. The heart is 

 tied to a simple cannula 

 (Fig. 122, A) introduced into 

 the cavity of the ventricle 

 through an opening in tin- 

 sinus venosus. Owing to its 

 structure, it is easy to study 

 the effect of successive liga- 

 tures applied at different 

 recording heights of the auricles, when 

 the heart is fixed in the tono- 

 graphic apparatus. Since 

 the same nutrient fluid leaves 

 the heart at each systole and 

 re-enters it at each diastole, 

 the renewal of the solution 

 can only be effected slowly 

 by diffusion through the 

 supernatant fluid, and filtra- 

 tion through the vessel walls. 



This is a great drawback when the heart is to be kept for any length of time 

 under constant and normal conditions of nutrition. Under these circum- 

 stances it is necessary to replace the simple cannula by the two-way cannula 

 of Kronecker, figured in 122, B. An improvement on Kronecker's apparatus 

 is that of Williams (Fig. 123). This provides for the circulation of the nutritive 

 solution, by the complete separation of the fluid which enters, from that 

 which leaves, the heart, by means of two valves for its entrance and exit. 

 If the frog's heart is to be attached to the apparatus by a cannula introduced 

 into the ventricle through the aortic bulb, it is necessary to supplement 

 Kronecker's irrigation cannula by a verv fine connecting tube, as shown in 

 Fig. 122 C. 



The tonographic method introduced by Oehrwall (1896) is much simpler 

 By this it is possible to obtain simultaneous tracings of the activity of the 



