142 Journal of Agriculture. [10 March, 1909. 



are known as Peyer's patches. Then in connexion with the coecum there 

 is a definite mass of this tissue which in some animals (as in inan) is so 

 pronounced as to constitute a distinct org^n, the vermiform appendix. 

 Of the functions performed by these lymphoid organs we know nothing. 

 The only surmise possible is that they act antagonistically to invading 

 disease germs, but it must be admitted that they are themselves singularly 

 liable to bacterial aggression ; thus, as in the human being, the tonsil 'S 

 attacked by scarlatina and quinsy, Peyer's patches by typhoid, and the 

 appendix by various inflammatorv processes. 





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Fif^. 64. — Part of a section of the human thyroid — a, fibrous capsule ; b , thyroid 

 vesicles filled with, e, colloid substance; c, supporting fibrous tissue; d, short 

 columnar cells lining vesicles; /, arteries; g, veins filled with blood; h, lymphatic 

 vessels filled with colloid substances. (After S. K. Alcock.) 



THE SPLEEN. — This organ, present in all true vertebrates, is com- 

 posed of a tissue closely resembling lymphoid tissue. It is well supplied 

 with blood vessels and its cells come into closer contact with blood than 

 those of almost any organ of the body, as lymph spaces are practically 

 absent. The blood circulating through it passes eventually into the 

 portal vein and so must traverse the liver before reaching the general 

 circulation. It has been supposed that the function of the spleen is to 

 pick out of the blood the red corpuscles that are the worse for wear and 

 to destroy them, but the evidence on which this view is based is not con- 

 vincing. Some have supposed the spleen to be the seat of formation 

 of white blood corpuscles but this liypothesis rests chiefly on the fact 

 that in some diseases, such as malaria in which the white cells of the 

 blood nre increased, the spleen is swollen. An animal deprived of its 

 spleen suffers in no detectable manner. This however does not prove 

 the uselessness of the organ as its duties may be taken up bv other 

 tissues, in fact, some of the lymnhatic glands throughout the body have 

 portions of their structure remarknblv like the spleen in appenrance, and 

 it has been coniectured that these glands can undertake the spleen's duties, 

 ■when this organ is removed. 



