LYMPHATIC SYSTEM AND DUCTLESS GLANDS. 357 



cells in which are often found one or more red corpuscles 

 which have apparently been swallowed by them. There are 

 also many pigmented granules, some free and some within 

 amosboid cells; they are apparently the debris of red corpus- 

 cles which have been broken down. In early life the splenic 

 pulp also contains granular colorless cells within which red 

 corpuscles are seen in the process of development. The whole 

 histological structure of the adult pulp suggests that in it 

 many red blood-corpuscles are finally destroyed, setting free 

 haemoglobin and other coloring matters derived from it. This 

 breaking down of haemoglobin must also give rise to proteids 

 and substances derived from the chemical degradation of 

 proteids, and the spleen is extremely rich in nitrogenous 

 crystallhie^^ubatances. The increase in size of the spleen 

 during Tngestion, when the veins of the alimentary canal are 

 pouring great quantities of blood laden with absorbed mat- 

 .ters into the portal system, suggests that the spleen supplies 

 things to the liver at that time which, are of importance to it. 

 There is reason to believe that the main coloring matter 

 of the bile (bilirubvii) is derived from the haemoglobin of red 

 corpuscles which have completed their life-period and been 

 destroyed, and it may be that the spleen takes the first steps in 

 the preparation of bilirubin for its elimination from the Body 

 as a waste product. There still is, however, much doubt as 

 to the real function of the spleen; it almost certainly plays 

 an important part in the proteid metabolisms of the Body. 

 Though so large an organ it is not essential; animals from 

 whom it has been completely removed can live a long time 

 in good health. The red marrow of spongy bone greatly re- 

 sembles the splenic pulp in histological characters and may 

 have similar functions and be able to entirely take the place of 

 the spleen when the organ has been excised. The white spots 

 seen on the cut surface of a spleen are sections of masses of 

 adenoid tissue attached to the smaller splenic arteries and 

 named MalpigMan corpuscles; they resemble the elosed fol- 

 licles of the intestine in structure. 



The Thyroid Body or Gland. This organ lies in the 

 neck on the sides of the windpipe and consists usually of a 

 right and a left lobe united by a narrow isthmus across the 

 front of the air-tube. It is about thirty grams (two ounces) 

 in weight; in the disease known as goitre it is greatly en- 

 larged and its structure altered. The thyroid is dark red in 



