332 SECRETION. 



this idea, these organs have been called blood-glands, or vas- 

 cular glands; but inasmuch as the supposition that these 

 parts effect changes in the blood or lymph is merely to sup- 

 ply the want of any definite idea of their function, and rests 

 mainly upon analogy with certain of the functions of the 

 liver, we shall retain the name, ductless glands, as indicating 

 the most striking of their anatomical peculiarities. 



As far as presenting any definite and important physio- 

 logical information is concerned, we might terminate here 

 the history of the ductless glands. It is true that the 

 largest of them, the spleen, has been extensively experi- 

 mented upon by the earlier physiologists ; but in point of 

 fact, investigations have done little more than exhibit a want 

 of knowledge of the functions of these remarkable organs ; 

 and the literature of the subject is mainly a collection of 

 wild speculations and fruitless experiments. There are, 

 however, some interesting experimental facts with relation 

 to the spleen and the suprarenal capsules ; though they are 

 not very instructive, except that they indicate the extremely 

 narrow limits of our positive knowledge. These few facts, 

 with a sketch of the anatomy of the parts, will embrace all 

 that we shall have to say concerning the ductless glands. 

 Under this head are classed, the spleen, suprarenal capsules, 

 thyroid gland, thymus, and sometimes the pituitary body 

 and the pineal gland. These parts have certain anatomical 

 points in common with each other, but on account of our 

 want of knowledge of their functions, it is difficult to distin- 

 guish, as we have done in other organs, their physiological 

 anatomy. 



Anatomy of the Spleen. 



The spleen is found, with but few exceptions, in all ver- 

 tebrate animals, but does not exist in the invertebrata. 1 It 



1 This organ, according to Van der Hoeven, is not found in the cyclostomes 

 and the lepidosiren (Handbook of Zoology, Cambridge, 1858, vol. ii., p. 29); and 

 Milne-Edwards states that it is absent also in the amphioxus (Lemons sur la 



