METABOLISM OF THE TISSUES. 367 



degeneration which occurs in the form of fatty globules or granules in albuminous tissues, e.g., 

 in muscular fibres (heart), gland-cells (liver, kidney), cartilage-cells, lymph- and pus-corpuscles, 

 as well as in nerve-fibres separated from their nerve centres. The fat in these cases is derived 

 from albumin, much in the same way as fat is formed in the gland-cells of the mammary and 

 sebaceous glands. Marked fatty degeneration not unfrequently occurs after severe fevers, and 

 after artificial heating of the tissues ; when a too small amount of is supplied to the tissues, 

 as occurs in cases of phosphorus poisoning {Bauer) ; in drunkards ; after poisoning with arsenic 

 and other substances, and after some disturbances of the circulation and innervation. Some 

 organs are especially prone to undergo fatty degeneration during the course of certain diseases. 



243. METABOLISM OF THE TISSUES. The blood-stream is the chief 

 medium whereby new material is supplied to the tissues and the effete products re- 

 moved from them. The lymph which passes through the thin capillaries comes 

 into actual contact with the tissue elements. Those tissues which are devoid of 

 blood-vessels in their own substance, such as the cornea and cartilage, receive 

 nutrient fluid or lymph from the adjacent capillaries, by means of their cellular 

 elements, which act as juice-conducting media. Hence, when the normal circulation 

 is interfered with, by atheroma or calcification of the walls of the blood-vessels, 

 these tissues are secondarily affected [this, for example, is the case in arcus senilis 

 of the cornea, due to a fatty degeneration of the corneal tissue, owing to some affec- 

 tion of the blood-vessels on which the cornea depends for its nutrition]. Total com- 

 pression or ligature of all the blood-vessels results in necrosis of the parts supplied 

 by the ligatured blood-vessels. 



Atrophies caused by diminution of the normal supply of blood, gradually, in the course of time 

 become less and less (Sainuel). 



Hence, there must be a double current of the tissue juices ; the afferent or 

 supply current, which supplies the new material, and the efferent stream which 

 removes the effete products. The former brings to the tissues the proteids, fats, 

 carbohydrates, and salts from which the tissues are formed. It is evident that any 

 interruption of the arterial supply to the tissues will diminish this supply. 



That such a current exists is proved by injecting an indifferent, easily recognisable substance 

 into the blood, e.g., potassium ferrocyanide, when its presence may be detected in the tissues, 

 to which it has been carried by the outgoing current. 



The efferent stream carries away the decomposition products from the various 

 tissues, more especially urea, C0. 2 , H 2 0, and salts, and these are transferred as 

 quickly as possible to the organs through which they are excreted. 



That such a current exists is proved by injecting such a substance as potassium ferrocyanide 

 into the tissues, e.g., subcutaneously, when its presence may be detected in the urine within 

 two to five minutes. 



If the current from the tissues to the blood is so active that the excretory organs 

 cannot eliminate all the effete products from the blood, then these products are 

 found in the tissues. When certain poisons are injected subcutaneously, they pass 

 rapidly into the blood and are carried in great quantity to other tissues, e.g., to the 

 nervous system, on which they act with fatal effect, before they are eliminated to 

 any great extent from the blood by the action of the excretory organs. The effete 

 materials are carried away from the tissues by two channels, viz., by the veins and 

 by the lymphatics, so that if these be interfered with, the metabolism of the tissues 

 must also suffer. When a limb is ligatured so as to compress the veins and the 

 lymphatics, the efferent stream stagnates to such an extent that considerable swell- 

 ing of the tissues or oedema may occur ( 203). The action of the muscles and 

 fasciae are very important in removing these effete matters. 



H. Nasse found that the blood of the jugular vein is 0*225 per 1000 specifically heavier than 

 the blood of the carotid, and contains "9 parts per 1000 more solids; 1000 cubic centimetres 

 of blood circulating through the head yield about 5 cubic centimetres of transudation into the 

 tissues. 



The extent and intensity of the metabolism of the tissues depend upon a 

 variety of factors. 



