4 THE BLOOD. 



the deficiency caused by the retention of some blood in the capillaries, and in part by 

 transudation, that our estimate of the quantity of blood contained in the human body 

 may be considered as slightly below the actual quantity." 



The process just described gives the most accurate idea of the probable quantity of 

 blood in the human body ; and, although more recent investigations have been made 

 upon the lower animals, by different methods, they are all more or less open to objec- 

 tion. We may assume, then, that, in a person of ordinary muscular and adipose devel- 

 opment, the proportion of blood to the weight of the body is about one to eight, the 

 entire quantity of blood in the body being from sixteen to eighteen pounds. The relative 

 quantity of blood is said to be less in the infant than in the adult, and to be diminished 

 in old age. It has been found, also, in observations on the inferior animals, to be greater 

 in the male than in the female. 



Prolonged abstinence from food, except when large quantities of liquid are ingested, 

 has a notable effect in diminishing the mass of blood, as indicated by the small quantity 

 which can be removed from the body, under these circumstances, with impunity ; and it 

 has been experimentally demonstrated that the entire quantity of blood is considerably 

 increased during digestion. Bernard drew from a rabbit weighing about two and a half 

 pounds, during digestion, over ten and a half ounces of blood without producing death ; 

 while he found that the removal of half that quantity from an animal of the same size, 

 fasting, was followed by death. Wrisberg has reported a case of a female criminal, very 

 plethoric, from whom twenty-one pounds, seven and three-quarters ounces of blood 

 flowed after decapitation. As the relations of the quantity of blood to the digestive 

 function are so important, it is unfortunate that the conditions of the system in this 

 respect were not noted in the observations of Lehmann and Weber. It is evident, there- 

 fore, that the quantity of blood in the body is considerably increased during digestion ; 

 but as regards the extent of this increase, we cannot form any very definite idea. It is 

 only shown that there -is a marked difference in the effects of haamorrhage in animals, 

 during digestion and fasting. 



General Characters of the JBlood. 



Opacity. The opacity of the blood depends upon the fact that it is not a homogene- 

 ous fluid, but is composed of two distinct elements, a clear plasma and corpuscles, which 

 are both nearly transparent, but which have a different 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 refracted in passing from the air 

 to 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 following simple experiment : If 

 to a little chloroform colored red, clear water be added in a test-tube, these liquids re- 

 main distinct from each other, and both are transparent ; but if we agitate them vio- 

 lently, the chloroform is temporarily subdivided into globules and mixed with the water ; 

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



Odor, Taste, Reaction, and Specific Gravity. The blood has a faint but characteristic 

 odor. This may be developed so as to be very distinct by the addition of a few drops 

 of sulphuric acid, when an odor peculiar to the animal from which the blood has been 

 taken becomes very marked. 



The taste of the blood is faintly saline, on account of the presence of a considerable 

 proportion, three or four parts per thousand, of chloride of sodium in the plasma. 



The reaction of the blood is always distinctly alkaline. According to Zuntz, the 

 alkalinity diminishes rapidly after the blood is drawn from the vessels. The alkaline 

 reaction is due to the presence of basic carbonate and phosphate of soda in the plasma. 



The; specific gravity of defibrinated blood is from 1052 to 1057 (Robin), being some- 



