STRUCTURE OF THE HUMAN BODY 



43 



The so-called ductless giands are related to the lymph -system. 

 The largest of them is the dark -red milt or spleen (fig. 13), 

 situated close to the stomach. It has to do with the destruction 

 of worn-out red corpuscles. The thyroid 

 gland is closely applied to the ventral side 

 of the larynx, and is notorious as the organ 

 which swells up in cases of Derbyshire neck 

 (goitre). It has been proved to be of impor- 

 tance in regulating the nutrition of the body. 

 The thymus gland is a fatty-looking mass 

 wrapped round the base of the heart, and 

 much larger in infants than in adults. In 

 the early stages of life it is one of the chief 

 sources of colourless corpuscles. 



Lymphatic glands are little swellings 

 placed here and there in the course of lym- 

 phatics (fig. 19). New colourless corpuscles 

 are constantly being formed in them. 



WASTE-REMOVING ORGANS 



* 



The living substance making up the body 

 of an animal is constantly undergoing a 

 process of change, whereby it breaks down Glands *\ the inner side of the 



elbow, ab; in the arm-pit, ccc', on 



into simpler compounds. We have, in fact, the chest In front of the arm-pit, 



r 1 . 1 1 , . d'> above the collar-bone and com- 



two sets of chemical changes constantly going municating with the arm-pit, e /. 



. , . , . gg point to lymphatic vessels form- 

 On Within the body: ing an arch round the hand. The 



/ \ . r i *l i* dark lines are lymphatic vessels. 



(a) A series of upbuilding or constructive 



processes whereby the food is gradually converted, step by step, 

 into the substances which constitute the body, and of which the 

 most complex is the living material known as protoplasm. This 

 series of chemical changes is comprised under the head of 

 assimilation (L. adsimilo, I make like), i.e. processes whereby the 

 body makes the material taken in as food into fresh substance 

 like itself. Assimilation is most naturally dealt with under the 

 head of Nutrition. 



(ft) The other set of chemical changes within the body are 

 destructive in nature, involving the down-breaking of material, 

 partly of protoplasm itself, and partly of other less complex 

 compounds. These changes have been called "local death", and 



