450 THE METABOLISM OF THE TISSUES. 



The activity of metabolism in the tissues and at the same time the in- 

 tensity in the varying currents depends upon diverse factors : 



1. Upon the activity of the tissues themselves. The increased activity of an 

 organ can be recognized from the larger amount of blood contained in it and the 

 increased activity of the circulation, which in turn are the media for the metab- 

 olism. If an organ is subjected to complete inactivity, for example a paralyzed 

 muscle or the peripheral extremity of a divided nerve, the amount of blood an'd its 

 interchange soon diminish. The organism sends its fluids only to active tissues. 

 The affected part becomes pale and flaccid and finally undergoes fatty degenera- 

 tion. For some organs increased metabolism in association with their activity 

 has been demonstrated, for example the muscles. Langley and Sewall have 

 been able to observe microscopically the metabolism in thin lobules of 

 glands during life. The cells both of the serous and of the mucous and peptic 

 glands become filled in the state of rest with coarse granules, dark in transmitted 

 and white in reflected light, which are consumed during the period of activity. 

 During sleep, in which most of the organs are at rest, metabolism is restricted. 

 It is likewise diminished by darkness, while it is stimulated by light (obviously 

 through nervous influences). The variations in total metabolism will be 

 reflected in the elimination of carbon dioxid and urea, which in conformity with 

 the activity of the organism yields a curve that is fairly parallel with that for 

 the daily variations in respiration, pulse and temperature. 



2. Also the state of the blood has a distinct influence upon the currents in the 

 tissues on which the metabolism depends. A highly concentrated blood deficient 

 in water (such as is observed after profuse sweating, copious diarrhea, for example 

 in cases of cholera) renders the tissues dry; while, conversely, the taking up into 

 the blood of large amounts of water renders the tissue more succulent, even to 

 the point of dropsy. The presence of a considerable amount of sodium chlorid 

 in the blood and a reduction in the amount of oxygen in the red blood-corpuscles, 

 the latter in association with muscular exertion causing dyspnea, give rise to 

 increased disintegration of albuminates and thus to increased production of urea. 

 Therefore, exposure to rarefied air causes increased elimination of urea. Certain 

 abnormal changes in the blood are noteworthy: Thus, carbon-monoxid blood is 

 not capable of abstracting oxygen from the air and conveying carbon dioxid from 

 the tissues. The presence of hydrocyanic acid in the blood immediately interrupts 

 the chemical oxidation-processes carried on through the blood; the tissues no 

 longer remove oxygen from the bright-red blood overladen with oxygen, and 

 there thus results asphyxia from interference with the internal respiration. Fer- 

 mentative processes also are interfered with in the same way by hydrocyanic acid. 

 A reduction in the total volume of blood causes, on the one hand, the passage of 

 a larger amount of water from the tissues into the vessels, while, on the other hand, 

 it retards the absorption of substances from the tissues (for example, poisons or 

 pathological exudates) or from the surface of the intestine. If the substances 

 derived from the tissues are rapidly eliminated from the blood, or transformed 

 therein, subsequent absorption takes place the more rapidly. 



3. The blood-pressure has an influence upon the fluid-current, inasmuch as 

 marked increase of pressure renders the tissues richer in fluid, but the blood itself 

 more concentrated (up to from 3 to 5 in 1000). That pressure upon the afferent 

 vessels causes the escape of blood-plasma through the walls of the capillaries can 

 be demonstrated on a surface of corium denuded of its epidermis, as, for example, 

 in a blister. Reduction of the blood-pressure will have the opposite effect. After 

 administration of phosphorus, copper, ether, chloroform, and chloral, the oxidation- 

 activity in the animal body is diminished. 



4. Elevation of the temperature of the tissues (for several hours during the day) 

 does not cause increased destruction of proteid and fat. This subject is discussed 

 also on pp. 404, 406 and 409. 



5. An influence of the nervous system upon the tissue-metabolism has also been 

 observed. Doubtless this influence is a double one. In the first place it may be 

 exerted indirectly through the intermediation of the vessels, the vascular nerves 

 causing contraction or dilatation of the vessels, and thus increasing or diminishing 

 the amount of blood passing through the vessels. In this connection attention 

 should be called especially to pathological conditions, abnormal stimulation or 

 paralysis of the vascular nerves or their centers. Independently of the vessels, 

 however, certain special nerves that have been designated trophic control the 

 metabolism in the tissues. Atrophy caused by nerve-paralysis increases the longer 

 it persists. Examples of metabolism in tissues excited directly through the nerves 

 are the secretion of saliva on nerve-irritation after exclusion of the circulation 



