346 DUCTLESS GLANDS. 



is usually followed by negative results ; and he states that if the 

 parathyroids are removed from these animals together with the 

 thyroid, the usual results appear. On the other hand, Blumen- 

 reich and Jacoby state that it makes no difference whether the 

 parathyroids are included or excluded. 



THE THYMUS. 



The thymus is situated behind the sternum, and extends from 

 the fourth costal cartilage to the lower border of the thyroid. It 

 is about 5 cm. long, about 4 cm. broad, and 1 cm. thick, and at 

 birth weighs about 16 grams. 



The thymus reaches its full size at the end of the second year, 

 at which time it decreases, and at puberty it has almost wholly dis- 



jliiiilla 





FIG. 188. A small lobule from the thymus of a child, with well-developed cortex, 

 presenting a structure similar to that of the cortex of a lymph-gland : a, hilus ; b, 

 medullary substance ; c, cortical substance ; d, trabecula ; X 60 (Bohin and Davidoff ). 



appeared ; it is, therefore, a temporary organ. The thymus of the 

 calf is called the neck or throat-sweetbread, while the pancreas 

 is the belly-sweetbread. 



Chemical Composition. The reaction during life is alka- 

 line, but acid after death, due to sarcolactic acid. It contains 

 12.29 per cent, of proteids, together with adenin, xanthin, hypo- 

 xanthin, and guanin. lodin exists also in the gland. 



Structure. The thymus is composed of two lobes, sometimes 

 united into one and sometimes separated by an intermediate lobe. 

 It presents an irregular lobulated appearance, and has an external 

 capsule, beneath which are the lobules, separated from one another 

 by connective tissue, in which are the blood-vessels and lymphatics. 

 Each lobule is made up of a cortex and medulla ; the cortex being 

 composed of nodules separated by trabeculce, as described in con- 

 nection with the lymphatic glands (p. 332). In the nodules are 

 lymphoid cells and a reticulum (Fig. 188). In the medullary 

 portion the lymph-corpuscles are less numerous, but there are here 



