104- THE BLOOD. 



respect were not noted; a circumstance which would have 

 added materially to their value. 



It is thus evident that the quantity of blood in the body 

 is considerably increased during digestion ; but as to the 

 extent of this increase, we cannot yet form any definite idea. 

 It is only shown that there is a very marked difference in 

 the effects of hemorrhage in "animals, during digestion and 

 fasting. 



The reaction of the blood, which has been determined 

 after the globules have separated so as to allow the applica- 

 tion of test paper to the clear plasma, has been found to be 

 uniformly alkaline. 



Physical Characters of the Blood. 



Opacity. One of the first physical characters of the blood 

 which attract our attention is its opacity. This depends 

 upon the fact that it is not a homogeneous fluid, but com- 

 posed of two distinct elements : a clear plasma, and corpus- 

 cles, which are nearly as transparent, but which have a dif- 

 ferent refractive power. If both of these elements had the 

 same refractive power, the mixture would present no obstacle 

 to the passage of light ; but as it is, the rays, which are bent 

 or refracted in passing from the air through the plasma, are 

 again refracted when they enter the corpuscles, and again 

 when they pass from the corpuscles to the plasma, so that 

 they are lost, even in a thin layer of the fluid. This loss of 

 light in a mechanical mixture of two transparent liquids of 

 unequal refractive power can be demonstrated by the fol- 

 lowing simple experiment. If to a little chloroform, col- 

 ored red, clear water be added in a test-tube, these liquids 

 remain distinct from each other, and are both transparent ; 

 but if we agitate them violently, the chloroform is tempo- 

 rarily subdivided into globules and mixed with the water ; 

 and as they refract light differently, the mixture is opaque. 



Odor. The blood has a faint but characteristic odor. This 



