14 CIRCULATION OF THE BLOOD DIAGRAM 1. 



is generally represented of this 

 colour, which is that of the veins 

 which can be seen under the skin, 

 either on the back of the hand or 

 foot, or at the fold of the elbow. 

 But when one of these blue veins 

 is opened, as in bleeding, to draw 

 blood from it, it is seen to be of 

 a very dark red. It does not run 

 with much force. If, on the con- 

 trary, a wound has unfortun- 

 Heart cut open. ate iy opened an artery, the blood 



spurts out to a distance of several yards, and it is seen to be of a 

 vermillion red. The blood has this colour when it has been to the 

 lungs, and has taken up the oxygen of the air derived from respi- 

 ration ; it loses this fine red colour in proportion as it deposits this 

 oxygen in the tissues. Consequently, when a man is suffocated, he 

 turns blue, as we say, because all his blood is of the colour of that 

 in the veins. 



The heart never ceases to beat from birth to death, in order 

 to drive the blood into the arteries ; it beats about 75 to 80 

 times in a minute, but sometimes much less ; when it beats 

 quicker it is a symptom of fever. The beatings of the heart can 

 be counted by laying the hand on the chest, but as the pulsation 

 is communicated to all the arteries, it is easier to feel it in those 

 parts of the body where the arteries do not lie very deep. It 

 is so at the wrist ; and this is the place where doctors 

 generally count the pulse. The beating will be found by drawing 

 the finger once or twice above the bend of the wrist, from the 

 side of the palm of the hand towards that side of the fore-arm 

 which corresponds to the thumb. 



The heart is somewhat conical in shape ; it contains several 

 divisions or chambers through which all the blood successively 

 passes. It drives the blood to the lungs, where it becomes red ; 

 and the blood then returns to the heart, which drives it through 



