CHAPTER IT. 



THE BLOOD. 



SEC. 1. THE PHYSICAL CHARACTERS OF THE BLOOD. 



Physical THE blood as it circulates in the vessels of man 

 and vertebrates generally is a viscous, and to the naked 

 eye homogeneous liquid of red colour : the blood of the pul- 

 monary veins, of the left side of the heart, and of the systemic 

 arteries being normally of a bright scarlet hue, and the blood 

 of the right side of the heart, of the systemic veins, and of the 

 pulmonary artery being of a brownish-red colour. On exposure to 

 air or to oxygen the brown-red colour of venous blood soon changes 

 to scarlet, and this change takes place most rapidly when the blood 

 and gas are shaken up together. 



In order to collect for purposes of analysis or demonstration pure arterial 

 or venous blood, or both, so as to avoid contact with air, the following 

 apparatus or some modification of it may be employed : 



A and B are two glass tubes of about 100 c.c. capacity, which at their 

 lower extremities are connected by means of elastic tubing with a forked 

 tube 0, to which is attached the elastic tube D, which at its other end is 

 connected with the glass bulb 7?, having a capacity of about 250 c.c. At 

 their upper extremities, A and B have connected with them two glass stop- 

 cocks, the tubes leading from which are of narrow diameter ; it is convenient 

 that these tubes should be of such a size that india-rubber tubing of 

 narrow diameter can easily be attached to them. The tubes are fixed in 

 two separate iron clamps such as are shewn in the drawing, attached to a 

 firm upright rod of iron with a firm stand. The reservoir R is also 

 held by a similar clamp, which can easily be attached either to the top or 

 to the bottom part of the upright rod, so as to place it above or below any 

 given level in relation to the tubes A and B. 



The reservoir being, say, in the lower position indicated in the figure, 

 mercury is poured into it so as to fill it. It is next undamped and raised 



