446 MATERIA MEDIC A AND THERAPEUTICS. 



CHAPTER VIII. 



THE BLOOD. 



WE will now suppose that the products of absorption and 

 hepatic metabolism have entered the blood. The peculiar rela- 

 tions which the blood bears to the solid organs gives a special 

 character to its pathology and therapeutics. It possesses of 

 itself no active functions, but is simply a great fluid medium 

 which conveys nutrient material and oxygen to the tissues, and 

 carries away the products of their activity. In the same way it 

 is the medium by which the active principles of drugs reach the 

 internal organs, without, as a rule, materially disturbing the 

 functions of the blood itself. It is not surprising that the blood 

 should have comparatively few primary disorders, whilst it is 

 constantly liable to suffer in consequence of disease of the 

 digestive organs from which we have traced its supply, and 

 of the excreting organs by which its constituents finally leave 

 the body. 



I. PHYSIOLOGICAL RELATIONS. 



The physiological relations of the liquor sanguinis are very 

 obvious : it is the medium of nutrition. It carries between 

 the different organs the materials which are the sources of 

 energy, namely albumins, fats, sugar, water, and salts, as well 

 as the products of the vital processes carbonic acid, water, urea, 

 salts, and other substances. It possasses a mean volume, an 

 alkaline reaction depending on the presence chiefly of salts of 

 soda, and a certain general uniformity of composition, which, 

 however, varies considerably at different parts of the circula- 

 tion for instance, before and after exposure of the blood to 

 the liver, lungs, muscles, or other active organs. The compo- 

 sition of the liquor sanguinis is indeed the balance of two 

 opposed processes a process of supply, income, or ingestion, 

 which we have traced through the liver from the food ; and 

 a process of production, expenditure, or egestion, carried on 

 by the active organs of the body, with their measurable pro- 

 ducts, energy and excretions. The white corpuscles are physio- 

 logically associated with the plasma, that is, are essentially 

 nutritive, in function ; but are probably also the source of the 

 red corpuscles. 



The function of the red corpuscles is perfectly distinct from 

 the functions of the plasma. They are the great medium of 

 respiration, carrying oxygen from the lungs to the tissues, and 

 are thus the respiratory elements of the body. It is important 



