ELEMENTARY EXPERIMENTAL PHYSIOLOGY 131 



corpuscles in a square with the percentage of the haemoglobin, the 

 worth of the corpuscle in haemoglobin is obtained. 



= ' worth ' of corpuscles. 

 Mo. in sq. 



The average number of red corpuscles is 5,000,000 per 1 c.mm. ; of 

 white, 10,000 per 1 c.mm. 1 



Specific Gravity of the Blood. A number of test tubes are taken 

 and filled with mixtures of glycerine and water, which vary in specific 

 gravity from 1030 to 1075. A pipette is taken with the point bent 

 at a right angle. The skin is pricked behind the finger nail, and a 

 drop of blood is drawn into the pipette. The blood is blown in small 

 droplets into the middle of the solution in several of the test tubes 

 until the solution is found in which the blood neither sinks nor rises. 

 The specific gravity of this solution is determined with the hydrometer. 

 The behaviour of the droplet must be noted at the moment when it 

 enters the solution. The blood quickly alters owing to osmotic change. 

 The specific gravity of the blood is about 1060, of the plasma 1026-29. 

 The specific gravity of fragments of muscle or other tissues may be 

 determined in the same way. The method is thus employed to deter- 

 mine the amount of tissue-lymph in the organs. 



CHAPTER XXXIV. 

 CIRCULATION OF THE BLOOD (ELEMENTARY DEMONSTRATIONS). 



Proofs of the Circulation of the Blood. A mammal is anaesthetised 

 with ether and chloroform. 



The external jugular vein is exposed and the carotid artery. A clip 

 is placed on the jugular vein. Note the central end of the vein 

 empties, while the peripheral end becomes enlarged. A clip is next 

 placed on the carotid artery, the central end becomes distended and 

 pulsates, while the peripheral end shrinks and ceases to pulsate. The 

 clips are now removed and two ligatures placed in position (but not 

 tied) under each vessel. The vein is pricked, Note the dark blood 

 which flows out from the peripheral end steadily and without force. 

 The vein is then tied above and below the opening. The artery is 

 next pricked. Note the blood spurts out forcibly and in jets from the 

 central end. The artery is then tied above and below the opening. 



1 After using, clean the pipettes of these instruments. Suck water, alcohol, and 

 ether up them in turn, and let the liquids run out. Never blow down the pipettes. 



