150 PRINCIPLES OF PHYSIOLOGY 



the ileum. These organs all agree anatomi- 

 cally in having no duct Hence, they are 

 sometimes called the ductless glands. It is a 

 misnomer to call them glands, as they are not 

 in any sense true glands, and they would be 

 more aptly designated " body " or " bodies." 

 All those organs that belong to the lymphatic 

 system proper contain a peculiar kind of 

 tissue, known as lymphoid tissue (found also 

 in the marrow of bone and below mucous 

 surfaces), consisting of a network of fine 

 fibres, with small masses of protoplasm at the 

 junctions of the fibres, as if the tissue were 

 formed of star-shaped cells, the rays of which 

 unite or anastomose to form a network. These 

 lymphatic bodies are concerned in the develop- 

 ment and growth of colourless cells of the 

 blood, but it is probable they have other 

 hidden functions at present unknown. 



80. The other bodies above mentioned are 

 now known to form what have been termed 

 internal secretions, which have important 

 physiological effects. Thus the thyroid body 

 forms a chemical substance, now known as 

 thyroidin, which contains iodine, and which 



