1 86 A MANUAL OF PHYSIOLOGY. 



period, and will be stronger and last for a longer time than in the 

 sodium chloride solution alone. 



(4) Immerse a fresh strip in a solution containing sodium chloride 

 (o'y per cent.), calcium chloride (0^025 P er cent.), and potassium 

 chloride (0*03 per cent.) (a modified Ringer's solution). A longer 

 series of rhythmical contractions will be obtained than in either (i) 

 or (3). That this is not due to the potassium chloride acting alone 

 can be shown by immersing a strip in a solution of potassium chloride 

 (about o'g per cent.) isotonic with the sodium chloride solution used 

 in (i). No contractions will be caused. 



13. The Action of the Mammalian Heart. -Inject under the skin of a 

 dog (preferably a small one) I c.c. of a 2 per cent, solution of morphine 

 hydrochlorate for every kilo of body- weight. As soon as the morphine 

 has taken effect (in 15 to 30 minutes, but, better, after an hour), fasten 

 the animal back down on a holder (as in Fig. 129, p. 288), pushing the 

 mouth-pin behind the canine teeth and screwing the nut home.* In 

 the meantime select a tracheal eannulaf of suitable size, and get ready 

 instruments for dissection one or two pairs of artery-forceps, a pair 

 of artery-clamps (bulldog pattern), two or three glass cannulae of 

 various sizes for bloodvessels, ten strong waxed ligatures, sponges, 

 hot water, a towel or two, and a pair of bellows to be connected 

 with the tracheal cannula when the chest is opened. Arrange an 

 induction-coil and electrodes for a tetanizing current (Fig. 81, p. 184). 

 With scissors curved on the flat clip away the hair from the front of 

 the neck. Put the hair carefully away, and remove all the loose 

 hairs with a wet sponge so that they may not get into the wounds. 

 Give ether, or pour into the stomach by a tube 5 c.c. of a 0-5 per 

 cent, solution of chloroform in 10 per cent, alcohol per kilo of body- 

 weight, diluted before administration with 3 or 4 volumes of water 

 (Grehant's method). 



To put a Cannula in the Trachea. The hair having been clipped in 

 the middle line of the neck and the skin shaved, a mesial incision 

 is to be made, beginning a little below the cricoid cartilage, which 

 can be felt with the finger. The trachea is then cleared from its 

 attachments by forceps or a blunt needle, and two strong ligatures 

 are passed beneath it. A single loop is placed on each of these 

 but is not drawn tight. Raising the trachea by means of the upper 

 ligature, the student makes a longitudinal incision through two or 

 three of the cartilaginous rings, inserts the cannula, and ties the 



* A simple but efficient and convenient holder for a dog may be easily 

 constructed as follows. Take a board of the length required (2^ to 5 feet, 

 according to the size of the dog) . At one end fasten two short upright 

 wooden pins, with a clear space of 4 to 6 inches between them. These 

 are pierced from side to side with four or five holes at different heights. 

 An iron pin passes behind the canine teeth of the animal through two 

 corresponding holes in the uprights, and the muzzle is tied over this by 

 a cord which secures the head. For a large dog an upper pair of holes 

 is used, for a small dog a lower pair. The feet are fastened by cords 

 to staples inserted into the sides of the board, the fore-legs being drawn 

 tailwards for all operations on the neck or head, headwards for operations 

 on the thorax. A rabbit-holder can be made in exactly the same way. 



f A tracheal cannula is easily made by heating a piece of glass tubing, 

 about 6 inches long, a short distance from one end, and drawing it out 

 slightly so as to form a ' neck.' The tubing is then bent about its middle 

 to an obtuse angle, and the end next the neck is ground obliquely on a 

 stone. The diameter of the cannula should be about the same as that of 

 the trachea, into which it is to be inserted by its oblique end. 



