Elements of Human Physiology (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III BLOOD AND LYMPH We have seen that the blood, which circulates through all parts of the living body, coming into close relationship with all the tissues, acts as a medium of communication between the cells in the interior of the body and those on the surface, carrying the absorbed foodstuffs which have been taken up by the cells lining the alimentary canal, to all the other cells of the body, and from these taking in exchange their waste products, C(X and urea or some precursor of these substances, to discharge them through the intermediation of excretory cells on the surface, or lining involutions of the outer surface of the body, such as the kidney, skin, and lungs. It is evident that the composition of the blood must be always varying, according to the nature of the tissues it has just traversed, and these variations will be more fitly considered when we come to the discussion of the activities of the various tissues. But we find that the blood has a certain power of regulating its composition, or perhaps this function must be ascribed to the various tissues through which the blood passes. However this may be, the fact remains that the blood has an average composition which it is our duty in this chapter to describe, and round which its composition only varies to a certain (definite) extent. The blood of man and most vertebrates is a redliquid, rather viscous, and to the naked eye homogeneous. Arterial blood, i. e. the blood in the pulmonary veins, left side of the heart, and the arteries generally, is bright scarlet, while venous blood, i. e. blood in the systemic veins, right heart, and pulmonary artery, is of a brownish-red hue. Shaking up venous blood with air or oxygen changes it to arterial, and we shall see later that the bright colour is due to...