280 FORMATION OF 



lymphatic system ; then, as the animal becomes larger, and of 

 consequence the lymphatic system more extended, that alone 

 and unassisted can now furnish a sufficient quantity of these 

 particles for the growth of the animal and repair of the con- 

 stitution ; the thymus being no longer necessary, and occupying 

 a space which by this time will become useful for other pur- 

 poses, the size of it will be gradually diminished, and its parts 

 absorbed into the habit. 



SECT, 93. The thymus gland is placed in the chest, because 

 the space it fills is not wanted by the foetus. After birth, 

 when respiration takes place and the animal increases in size, 

 the growth of the lungs requires the cavity of the chest to be 

 enlarged, which is done partly by the absorption of the thymus, 

 but chiefly by the extension of the ribs. 



SECT. 94. The thymus gland, then, we consider as being an 

 appendage to the lymphatic glands, for the more perfectly and 

 expeditiously forming the central particles of the blood in the 

 foetus, and in the early part of life (CXLJV). 



(CXLIV.) Bisclioff a partially supports Hewson's view as to the use 

 of the thymus. From a series of interesting observations, Mr. Simon 1 ' 

 includes its uses in the theory of fat-formation, concluding that 

 " the gland fulfils its use as a sinking fund of nourishment in the 

 service of respiration ;" and that, " what the gland sequestrates from 

 the circulation does, in gradually revisiting thither, accomplish those 

 chemical purposes in respect of respiration and temperature, which, 

 under other circumstances, are fulfilled by the effete products of active 

 animal tissues." He disbelieves, that the globules in the fluid can serve as 

 germs for the tissues or for the blood, because he declares it to be impossi- 

 ble that the globules, as such, can enter the lymphatic vessels without a 

 dissolution of the membrane lining the cells of the gland, and which, 

 he says, is a material of the most exquisite delicacy, rather a fine 

 boundary line than a membrane admitting of isolation. 



With respect to Mr. Simon's conclusion, it may be asked, if it has 

 yet been proved that the purposes of respiration and temperature are 

 fulfilled by the effete products of the animal tissues? In man and 

 several animals, there is commonly a larger proportion of fat in the 

 chyle than in the fluid of the thymus or of the lymphatic system ; and, as 

 mentioned in Note LX, p. 88, it is at least probable that fat performs an 

 important part in nutrition and growth. As to the impossibility of the 

 globules passing into the lymphatic vessels, it is now generally admitted 

 that the multiplication of floating cells is rapidly effected by the minutest 



a Mr. Simon's Essay on the Thymus, p. 9. b Physiol. Essay on the Thymus Gland, 



pp. 90, 91, 38, 34, 4to, Lond. 1845. 



