362 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



in from twenty-four to forty-eight hours if the loss of blood has been 

 severe ; but the number of red corpuscles and the haemoglobin are regenerated 

 more slowly, getting back to normal only after a number of days or after 

 several weeks. 



Blood-transfusion. Shortly after the discovery of the circulation of the 

 blood (Harvey, 1628), the operation was introduced of transfusing blood from 

 one individual to another or from some of the lower animals to man. Ex- 

 travagant hopes were held as to the value of such transfusion not only as a 

 means of replacing the blood lost by hemorrhage, but also as a cure for various 

 infirmities and diseases. Then and subsequently, fatal as well as successful 

 results followed the operation. It is now known to be a dangerous under- 

 taking, mainly for two reasons : first, the strange blood, whether transfused 

 directly or after defibrination, is liable to contain a quantity of fibrin ferment 

 sufficient to cause intravascular clotting ; secondly, the serum of one animal is 

 known to cause often a destruction of the blood-corpuscles of another. Owing 

 to this globulicidal action, which has previously been referred to (p. 334), the 

 injection of foreign blood is likely to be directly injurious instead of beneficial. 

 In cases of loss of blood from severe hemorrhage, therefore, it is far safer to 

 inject a neutral liquid, such as the so-called " physiological salt-solution " a 

 solution of NaCl of such a strength (0.9 per cent.) as to be isotonic to the cor- 

 puscles. The bulk of the circulating liquid is thereby augmented, and all the 

 red corpuscles are made more efficient as oxygen-carriers, partly owing to the 

 fact that the velocity of the circulation is increased, and partly because the 

 corpuscles are kept from stagnation in the capillary areas. 



LYMPH. 



LYMPH is a colorless liquid found in the lymph-vessels as well as in the 

 extravascular spaces of the body. All the tissue-elements, in fact, may be 

 regarded as being bathed in lymph. To understand its occurrence in the body 

 one has only to bear in mind its method of origin from the blood. Throughout 

 the entire body there is a rich supply of blood-vessels penetrating every tissue 

 with the exception of the epidermis and some epidermal structures, as the nails 

 and the hair. The plasma of the blood filters through, or is secreted through, 

 the thin walls of the capillaries, and is thus brought into immediate contact 

 with the tissues, to which it brings the nourishment and oxygen of the blood 

 and from which it removes the waste products of metabolism. This extravas- 

 cular lymph is collected into small capillary spaces which in turn open into 

 definite lymphatic vessels. These vessels unite to larger and larger trunks, 

 forming eventually one main trunk, the thoracic or left lymphatic duct, and a 

 second smaller right lymphatic duct, which open into the blood-vessels, each 

 on its own side, at the junction of the subclavian and internal jugular veins. 

 The lymph movement is from the tissues to the veins, and the flow is main- 

 tained chiefly by the difference in pressure between the lymph at its origin in 



