240 CIRCULATION OF THE BLOOD 



An increase or decrease of turgor in a certain part incident to different 

 positions of the body must evidently produce in other parts changes of an oppo- 

 site character. The volume of one arm is greater when the other is held pas- 

 sively above the head; the volume of the hand increases when both femoral 

 arteries are compressed, etc. Keflex activity of the vasomotor nerves often conies 

 in here to influence the result. 



B. THE INFLUENCE OF VASOMOTOR NERVES 



In general one may say that under normal circumstances every part of 

 the body receives exactly as much blood as it has need of, and that by dilata- 

 tion of vessels a particular part receives more blood the more active it is. 

 At the same time blood vessels in other parts of the body are constricted, and 

 in this way the normal blood pressure necessary for life is maintained by an 

 incessant reciprocity between the different vascular regions. 



In the state of bodily rest the organs of the thorax and abdomen contain a 

 relatively large part, as a rule more than half, of the total quantity of blood 

 in the body. The content of blood in these organs amounts to about twenty 

 per cent of their weight,, while the blood content of the skin, skeleton, muscles 

 and the nervous substances amounts to only two to three per cent of their 

 weight (Ranke et al). The blood stored up in the internal organs is always 

 at the disposal of any organ which has need of a larger supply. 



Thus in muscular work the vessels of the muscles and skin are dilated, while 

 at the same time the vessels innervated by the splanchnic nerve are constricted 

 to a greater extent. Consequently the blood pressure as a rule, if not always, 

 increases. 



By the use of apparatus constructed for the purpose of determining the 

 velocity of the blood, the quantity flowing through some of the organs in a given 

 time has been measured directly (cf. also page 211). In the dog Tschuewsky 

 found the quantity per minute and per 100 g. of organ to be 3.4 c.c. for the hind 

 limbs with the nerves intact, and 9.9 c.c. after section of the nerves. The head 

 received 16.6 c.c., muscles with uncut nerves 13 c.c., the thyroid gland 590.9 

 c.c. (!), all per minute and per 100 g. of organ. 



In the researches of Chauveau and Kaufmann the quantity of blood flowing 

 through the levator superiorus proprius muscle of the horse was : in rest, on the 

 average, 17.5 c.c. per 100 g. ; in activity, it rose to 85 c.c. According to Bohr and 

 Henriques, the dog's heart receives on the average 30 c.c. per minute per 100 g. 



In view of its function of removing from the body the nitrogenous products 

 of metabolism, the kidney receives a relatively large quantity of blood, especially 

 if great demands are made upon it by transfusion of a diuretic agent (cf. Chap- 

 ter XIII). There then flows through the kidney (dog) per minute a quantity 

 of blood which amounts to one hundred and forty per cent of its own weight 

 (average ninety-six per cent). In the same animal the quantity of blood expelled 

 from the left heart per minute may be estimated at about ten per cent of the 

 body weight. Hence, in strong diuresis the blood supply to the kidney would be 

 relatively fourteen times as great as to all the organs taken together. 



Furthermore the distribution of blood to the different parts of the body 

 exhibits incessant fluctuations produced by the vasomotor nerves, which are 

 connected either with the activity of the organs, or with the heat regulation of 

 the body; for the heat regulation is controlled in the main by vasomotor nerves 

 (cf. Chapter XIV). 



