86 THE CARDIO-PNEUMATIC MOVEMENT. 



it contracts. [According to Gaskell, antiarin and digitalin solutions produce an alteration in 

 the condition of the muscular tissue of the apex of the heart of the same nature as that pro- 

 duced by the action of a very dilute alkali solution, while the action of a blood-solution contain- 

 ing muscarin closely resembles that of a dilute acid solution (p. 95, 65).] 



[Nature of a Cardiac Contraction. The question as to whether this is a simple 

 contraction or a compound tetanic contraction has been much discussed. So 

 much is certain, that the systolic contraction of the heart is of very much longer 

 duration (8 to 10 times) than the contraction of a skeletal muscle produced by- 

 stimulation of its motor nerve. When the sciatic nerve of a nerve-muscle pre- 

 paration is adjusted upon a contracting heart, a single secondary twitch of the 

 limb, and not a tetanic spasm, is produced when the heart (auricle or ventricle) 

 contracts This of itself is not sufficient proof that the systole is a simple spasm, 

 for tetanus of a muscle does not in all cases give rise to secondary tetanus in the 

 leg of a rheoscopic limb. Thus, a simple " initial " contraction occurs when the 

 nerve is applied to a muscle tetanised by the action of strychnia, and the contracted 

 diaphragm gives a similar result. The question whether the heart can be tetanised 

 has been answered in the negative, and as yet it has not been shown that the 

 heart can be tetanised in the same way that a skeletal muscle is tetanised.] 



[Mac William finds, when the quadriceps extensor cruris contracts to cause the knee-jerk, that 

 a sound similar to the first sound of the heart is heard. As the former is regarded as a simple 

 contraction, it is argued that a simple contraction can produce a muscle-sound. Fredericq 

 regards the ventricular systole not as a simple contraction, but as composed of three or more 

 fused contractions corresponding to tetanus. This he concludes from a study of cardiograms as 

 well as from the electro-motive phenomena of the heart.] 



The peripheral or extra-cardiac nerves ( 369 and 370). 



59. CAEDIO-PNETJMATIC MOVEMENT. As the heart within the thorax 

 occupies a smaller space during the systole than during the diastole, it follows that, 

 when the glottis is open, air must be drawn into the chest when the heart contracts ; 

 whenever the heart relaxes, i.e., during diastole, air must be expelled through the 

 open glottis. But we must also take into account the degree to which the larger 

 intra-thoracic vessels are filled with blood. These movements of the air within the 

 lungs, although slight, seem to be of importance in hybernating animals. In 

 animals in this condition, the agitation of the gases in the lungs favours the 

 exchange of C0 2 and O in the lungs, and this slow current of air is sufficient to 

 aerate the blood passing through the lungs. [Ceradini called the diminution of the 

 volume of the entire heart which occurs during systole meiocardia, and the 

 subsequent increase of volume, when the heart is distended to its maximum, 

 auxocardia.] 



Method. A manomctric flame may be used. Insert one limb of a Y-tube into the opened 

 trachea of an animal, while the other limb passes to a small gas-jet, and connect the other tube with 

 the gas supply. The movements of the heart affect the column of gas, and thus affect the flame. 

 It may also be done in man by inserting the tube into one nostril, while the other nostril and 

 the mouth are closed. [A simpler and less irritating plan is to fill a wide curved glass-tube 

 with tobacco smoke, and insert one end of the tube into one. nostril while the other nostril and 

 the mouth are closed. If the glottis be kept open, and respiration be stopped, then the move- 

 ments of the column of smoke within the tube are obvious. Or a manometer containing a drop 

 of a coloured fluid may be used under the same conditions.] 



The cardiac pneumograph (fig. 64) consists of a tube (D), about 1 inch in diameter and 

 6 to 8 inches in length ; the tube is bent at a right angle, and communicates with a small metal 

 capsule about the size of a saucer (T), over which a membrane composed of collodion and castor 

 oil is loosely stretched. To this membrane is attached a glass rod (H) used as a writing-style, 

 which records its movements on a glass-plate (S) moved by clock-work. A small valve (K) is 

 placed on the side of the tube (D), which enables the experimenter to breathe when necessary. 

 The tube (D) is held in an air-tight manner between the lips, the nostrils being closed, the 

 glottis open, and respiration stopped. In the curves (fig. 64, A,B) we observe that 



(1) At the moment of the first sound (1) the respiratory gases undergo a sharp expiralory 

 movement, because at the moment of the first part of the ventricular systole the blood of the 

 ventricle has not left the thorax, while venous blood is streaming into the right auricle through 

 the venae cava?, and because the dilating branches of the pulmonary artery compress the 



