BLOOD AND H.EMOPOIETIC ORGANS 103 



the body than the Anglo-Saxon race would disappear 

 if the British isles became submerged. Most writers 

 are agreed* that the thymus attains its maximum 

 development relative to that of the body as a whole between 

 the second and fourth years of life, and it is interesting 

 to note that it is after this period that the lymphocytes 

 of the blood undergo a diminution in number. It 

 would appear as if more lymphocytes were wanted in the 

 earlier years of life, and that the thymus existed in order 

 to manufacture them ; but why they are wanted we do 

 not know. Excision of the gland throws little light on 

 the matter, most experimenters having found after it a 

 diminution of red cells and an increase of white. Nor 

 do we even know whether the presence of the organ in 

 the first years of life is essential to existence or even to 

 health. I know of only one case in which the thymus 

 was absent in an infant,t and in that case the child lived 

 until it was six months old, but as one kidney was absent 

 also, this case is of little value as evidence. 



Physiology and pathology are here alike at fault. 

 Neither has succeeded in showing that the thymus is 

 more than a mere mass of adenoid tissue. 



The lymphatic glands are, like the thymus, important 

 birthplaces of lymphocytes, and when they take on 

 increased functional activity, as in lymphatic leukaemia, 

 there ensues a great rise in the lymphocytic population 

 of the blood-stream. 



In addition to this they seem to help, at least, in the 

 protection of the body against invasion by bacteria or 



* Bonnet, Gaz. des Hopitaux, 1899, Ixxii. 1321. 

 t Reported by Alfred Clark, Lancet, 1896, ii. 1077. 



