208 THE HUMAN SPECIES 



the red bone-marrow where Naumann has found red blood 

 corpuscles containing haemoglobin and nuclei. All these condi- 

 tions suggest that in man and in other mammals there exists a 

 circulation of lymph, common also to birds, which is maintained 

 in movement by changes in the blood pressure in the capillaries, 

 as well as by respiratory and muscular movements : in reptiles 

 and amphibia there are, however, definite " lymph hearts " con- 

 trolling the circulation of lymph. 



The total mass of lymph is difficult to ascertain, the only 

 method available being by collection of the fluid from a lymph 

 fistula. A medium-sized dog produces per kilogramme and 

 hour about 2\ kilocentimetres of lymph. 



A horse (Colin) in 24 hours 16-42 kilogm. 



An ox 20-25 



A sheep 3-4! 



A man per hour 70-120 gm. 1 



Certain so-called vascular glands contribute to the circulation 

 " internal secretions," specific substances which exert regulating 

 or protective functions in the economy of the body. These 

 glands are the thyroid, the pituitary body (hypophysis), and the 

 adrenals. 



The thyroid gland secrets a colloid containing iodine from 

 which Baumann has isolated a proteid combined with iodine 

 (iodothyrin) ; the view now generally accepted is that the 

 function of this gland is to remove the nerve-toxines of the 

 general metabolism and to render them innocuous. This hypo- 

 thesis is based upon the observation that a man or animal whose 

 thyroid is completely removed dies by cachexia. When, as 

 sometimes chances, an animal survives total extirpation of the 

 thyroid (as rodents may), the explanation is to be found in the 

 existence of parathyroids capable of making good the loss. 



The pituitary body may act in like manner, but the proof 

 is not conclusive, for the destruction of this gland appears to 

 produce no symptoms : injection of its extract causes an im- 

 mediate fall in blood pressure, followed by a rise together with 

 a slower and more forcible beat of the heart. 



The adrenals yield from their medulla a substance soluble 

 in water (adrenalin), of which minute quantities injected sub- 



1 Munk-Schultz, loc. cit., p. 209. 



