368 METABOLISM OF THE TISSUES. 



1. Upon their activity. The increased activity of an organ is indicated by the 

 increased amount of blood going to it, and by the more active circulation through 

 it ($ 100). When an organ is completely inactive, such as a paralysed muscle, or the 

 peripheral end of a divided nerve, the amount of blood and the nutritive exchange 

 of fluids diminish within these parts. The parts thus thrown out of activity be- 

 come pale, relaxed, and ultimately undergo fatty degeneration. The increased 

 metabolism of an organ during its activity has been proved experimentally in the 

 case of muscle, and [( 263) also in the brain (Speck)]. Langley and Sewell have 

 recently observed directly the metabolic changes within sufficiently thin lobules of 

 glands during life. The cells of serous glands ( 143), and those of mucous, and 

 pepsin-forming glands ( 164), during quiescence, become filled with coarse granules, 

 which are dark in transmitted light and white in reflected light, which granules are 

 consumed or disappear during granular activity. During sleep, when most organs 

 are at rest, the metabolism is limited, darkness also diminishes it ; while light 

 excites it, obviously owing to nervous influences. The variations in the total meta- 

 bolism of the body are reflected in the excretion of C0 2 ( 127, 9) and urea ( 257), 

 which may be expressed graphically in the form of a curve corresponding with the 

 activity of the organism ; this curve corresponds very closely with the daily varia- 

 tions in the respirations, pulse, and temperature (p. 327). 



2. The composition of the blood has a marked effect upon the current on which 

 the metabolism of the tissues depends. Very concentrated blood, which contains 

 a small amount of water, as after profuse sweating, severe diarrhoea, cholera, makes 

 the tissues dry, while if much water be absorbed into the blood, the tissues become 

 more succulent and even cedema may occur. When much common salt is present 

 in the blood, and when the red blood-corpuscles contain a diminished amount of O, 

 and especially if the latter condition be accompanied by muscular exertion causing 

 dyspnoea, a large amount of albumin is decomposed, and there is a great formation 

 of urea. Hence, exposure to a rarefied atmosphere is accompanied by increased 

 excretion of urea. Certain abnormal conditions of the blood produce remarkable 

 results ; blood charged with carbonic oxide cannot absorb O from the air, and does 

 not remove C0. 2 from the tissues ( 16). The presence of hydrocyanic acid in the 

 blood ( 16) is said to interrupt at once the chemical oxidation processes in the 

 blood, so that rapid asphyxia, owing to cessation of the internal respiration, occurs. 

 Fermentation is interrupted by the same substance in a similar way. A diminution 

 <>f the total amount of the blood causes more fluid to pass from the tissues into the 

 blood, but the absorption of substances such as poisons or pathological effusions, 

 from the tissues or intestines is delayed. If the substances which pass from the 

 tissues into the blood be rapidly eliminated from it, absorption takes place more 

 rapidly. 



3. The blood-pressure, when it is greatly increased, causes the tissues to contain 

 more fluid, while the blood itself becomes more concentrated, to the extent of 3 to 

 5 per 1000. We may convince ourselves that blood-plasma easily passes through 

 the capillary wall, by pressing upon the efferent vessel coming from the chorium 

 deprived of its epidermis, e.g., by a burn or a blister, when the surface of the 

 wound becomes rapidly suffused with plasma. Diminution of the blood-pressure 

 produces the opposite result. The oxidation processes in the body are diminished 

 after the use of P, Cu, ether, chloroform, and chloral. 



4. Increased temperature of the tissues (several hours daily) does not increase 

 the breaking up of albumin and fats. (See 221, 220, 225.) 



5. The influence of the nervous system on the metabolism is twofold. On the 

 one hand, it acts indirectly through its effect upon the blood-vessels, by causing 

 them to contract or dilate through the agency of vaso-motor nerves, whereby it 

 influences the amount of blood supplied, and also affects the blood-pressure. But 

 quite independently of the blood-vessels, it is probable that certain special nerves 



