CHAPTER IX 



THYMUS, SPLEEN, PINEAL, MAMMARY GLAND AND 

 KIDNEY 



I have grouped in this chapter a number of or- 

 ins whose exact position in ductless glandular 

 classification is debatable. Some of the organs are 

 tot glandular in the histological sense. With 

 >thers we are not altogether certain that they pro- 

 Luce an internal secretion or, more correctly, a 

 specific hormone. A substance like carbon dioxide 

 is not produced by a gland, yet as a regulator of 

 respiratory activity and of the respiratory center it 

 ought, perhaps, to be discussed in this chapter. On 

 the other hand, a compound like urea is the prod- 

 uct of an organ of internal secretion ; but it is not 

 yet certain whether it has any direct influence on 

 the kidney. This chapter, then, is full of uncer- 

 tainties. 



THYMUS 



This organ is situated in the neck near the thy- 

 roid. It seems to be of particular importance in 

 the early life of the individual, though the most 



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