THE SPLEEN AND THYMUS. 411 



involved lymph- nodes and in the liver lesion. This condition has ap- 

 parently been several times described, but has been usually regarded as 

 turner rather than eudothelial hyperplasia. ' 



ALTERATIONS OF THE SPLEEN IN LEUKAEMIA AND PSEUDO- 

 LEUEJEMIA. 



The lesions of the spleen are essentially similar in both of these con- 

 ditions. They consist, in general, of an hyperplasia, sometimes most 

 marked in one, sometimes in another of the structural elements of the 

 organ, but they usually all participate in the alterations. The changes 

 which occur in the earlier stages are but little known. The gross ap- 

 pearances of the spleen vary. It is as a rule enlarged and sometimes is 

 ten or fifteen times the normal size. It is commonly hard, but is some- 

 times of the ordinary consistence, or softer, and the capsule is gener- 

 ally thickened and rough. The section of the spleen may be of a uni- 

 form dark-red color, but it is more frequently mottled red and gray. 

 Sometimes the glomeruli are inconspicuous, but' they are very often 

 enlarged and prominent. They may be two to four mm. in diameter, 

 and, owing to an infiltration of the arterial sheaths with lymph cells, 

 may appear to the naked eye as grayish, round or elongated bodies, 

 arranged along branching, interrupted, grayish streaks. The trabeculse 

 may be greatly thickened, as also the reticulum of the pulp, so as to be 

 evident to the naked eye. Brown or black pigment may be collected 

 around the glomeruli or in the pulp. Hsemorrhagic infarctions or cir- 

 cumscribed extravasations of blood may further complicate the picture. 



Microscopically the appearances are essentially the same as those 

 above described in acute hyperplasia and in chronic interstitial splenitis, 

 depending upon the stage and variety of the disease. Owing to the great 

 size which some of such spleens attain they are liable to displacement, and 

 they may interfere by pressure with the functions of neighboring organs. 



TUMORS. 



Primary tumors of the spleen are rare. Small fibromata, sarcomata, 

 and cavernous angiomata sometimes occur. Sarcoma and carcinoma may 

 occur in the spleen secondarily either as metastatic tumors or by exten- 

 sion from some adjacent part, as the stomach. Derm old cysts are de- 

 scribed, but are rare. Other larger and smaller cysts, whose mode of 

 origin is in most cases obscure, not infrequently occur. 



PARASITES. 



Pentastomum denticulatum is not infrequently found in the spleen, 

 usually encapsulated and calcified. Cysticercus is rare. Echinococcus is 



1 For details of this lesion, \vith bibliography, see Boraird, American Journal of the 

 Medical Sciences, vol. cxx., p. 377, 1900. 



