566 OF SECRETION. 



nucleus." Mr. Gulliver considers them identical (as Hewson did long ago) 

 with the chyle and lymph-globules. In the Human fetus, the fluid of the 

 Thymus Gland can scarcely be obtained in quantity sufficient for analysis : but 

 it has been found by Mr. F. Renaud,* that, on treating the sliced gland with 

 ether, a considerable quantity of oil was obtained from it ; so that the resem- 

 blance in its composition to chyle or milk is very close. In the Thymic fluid 

 of the Calf, which exists in greater abundance, the following ingredients were 

 found. One hundred parts of the fluid contained sixteen of solid matter; and 

 this consisted of incipient Fibrin, Albumen, Mucus and Muco-extractive mat- 

 ter, Muriate and Phosphate of Potass, Phosphate of Soda, and a trace of Phos- 

 phoric acid. 



712. Of the nature of the function of the Thymus Gland, nothing is cer- 

 tainly known. By Hewson it was regarded as an appendage to the system of 

 lymphatic glands ; and this doctrine is advocated by Mr. Gulliver. It is 

 remarked by Miiller, that it appears quite vain to attempt to explain by hypo- 

 thesis, how the organ can contribute to the formation of the blood in the foetus 

 and child ; and that " every hypothesis which regards it as an organ adapted 

 to the necessities of foetal life, and not to those of the child, must be incorrect." 

 This last observation appears to be pointed at the theory not long since put 

 forth by Mr. Tyson,t that the office of the Thymus is to receive, during Foetal 

 life, the blood which is afterwards sent to the Lungs; yet in support of this 

 theory something may still be said. It is well known that, although the Re- 

 spiratory function is established at birth, it does not for some time come into 

 full activity. The lungs are small in proportion to the size of the body ; the 

 amount of oxygen consumed is much less than in the adult state ; and the 

 power of generating heat is comparatively feeble ( 728). During infancy 

 and childhood, the Digestive apparatus is undergoing rapid development ; but 

 the Lungs do not make the same comparative progress. About the period of 

 puberty, however, their evolution becomes much more rapid, and their function 

 more energetic ; so that, at this time, as is well known, disorders of their 

 function, leading to structural changes, are more common than at any other 

 period of life. Now the relative disappearance of the Thymus Gland, pari 

 passu with the evolution of the lungs, does appear to indicate that there is 

 something vicarious or reciprocal in their function. Moreover, it has been 

 shown that one of these vascular masses, somewhat resembling glands in 

 structure, but having no secreting ducts, is found in connection with the two 

 other principal excretory organs, the Liver and the Kidneys. It may be 

 said, however, in reply, that the lungs do not receive their principal supply of 

 blood from the arterial system, but from the venous ; so that, although the two 

 organs are in proximity, there is no direct vascular connection between them. 

 This objection, however, has less force when it is remembered, that, up to the 

 time of birth, the period during which the Thymus gland is of greatest pro- 

 portional size, little or no blood proceeds to the Lungs through the Pulmonary 

 arteries ; but that they are then chiefly, if not entirely, supplied by the Bron- 

 chial arteries ; and these come off' from the thoracic aorta at no great distance 

 from the Internal Mammary arteries, which supply the Thymus gland, and are 

 the lowest branches of the Subclavian. It is through the Bronchial arteries 

 that the blood is conveyed, on which the nutrition of the Lungs depends, during 

 the whole of life ; and the history of the development of these organs, com- 

 pared with that of the Thymus gland, seems to indicate that, just as the flow 

 of blood through the one diminishes, that which takes place through the other 

 increases. It is, however, also true (as remarked by Mr. Gulliver) that the 



* Edinburgh Monthly Journal, March, 1843. 

 f London Medical and Surgical Journal, 1833. 



