

REGULATION OF CELL ACTIVITIES 191 



any cellular activity, acts on the respiratory centre in the 

 medulla, causing increased ventilation of the lungs, thus 

 favouring the removal of carbon dioxide from the blood.* 

 The carbon dioxide acts because it is an acid and raises the 

 hydrogen on concentration of the blood. 



TABLE XXXVI 



Composition of Nervous Tissue and of Muscle. 



Grey Matter f White Matter! Muscle \ 



Percent. Percent. Percent. 



Water 83-17 . 69-67 73-5 



Solids 16-83 



of which 



Protein . . . . 47-1 

 Extractives ... 9-5 



Ash 5-9 



Lecithins and Kephalins 23-7 



3 '33 



27-1 

 3'9 

 2-4 



31-0 



26-5 



67-8 

 0-83 

 n-7 



Lipoid S. as SO. . . o-l ' ' Fat 8 ' 6 



Cholesterin (by difif.) . 4-9 



Gelatin . . . . . . . 7-5 



The result is that the tension of carbon dioxide in the 

 alveolar air is kept constant, and as the production of carbon 

 dioxide is almost proportional to the use of oxygen the larger 

 amount of air required to remove more carbon dioxide during 

 tissue activity will bring enough oxygen into the lung alveoli. 



Urea, the main nitrogenous end product of the metabolism 

 of amino acids, acts on ,the kidney as diuretic, thus aiding 

 the removal of itself from the blood. 



Drugs administered to animals also act on the chemical 

 processes in the body. 



Over and above such instances of chemical regulation, 

 which is a common attribute of all cells, there are a number 

 of regulating substances produced by special organs. It is 

 these special organs that must be more especially studied in 

 this chapter. The organs which produce these internal 

 secretions are usually glandular in structure, but without 

 ducts to the exterior, hence they are called ductless glands, 

 and any secretion that they form is carried away by the blood 

 or lymph streams. 



THYROID GLAND 



Swelling of this gland with symptoms of mental dullness 



* J. S. Haldane and J. G. Priestley, Journ. Physiol., 1905, vol. 

 32, p. 225. 



f W. Koch and S. A. Mann, Journ. Physiol., 1907, vol. 36, proc., p. 

 xxxvi. 



$ W. D. Halliburton, Text Book of Physiology, edited by E. S. 

 Schafer, Pentland, 1898, vol. i, p. 95. 



