LYMPH NODES 75 



It should be added that some recent observations (1924) on 

 The Wistar Institute rats show a blood picture in agreement with 

 the authors who find the percentage values for the small lympho- 

 cytes about twice those for the polymorphonuclear cells. It 

 seems fair to conclude therefore at the moment that the blood 

 picture may vary in the rat as indicated above, and yet the 

 animals still breed well and grow vigorously. Why this wide 

 variation comes about is a question for further investigation. 



It should be noted in this connection that while both the 

 leucocytes and erythrocytes in the rat increase in number from 

 birth to maturity, in man the leucocytes show a great decrease 

 and the erythrocytes a slight decrease^ — Addison ('24 MS.). 



Lymph nodes. Concerning the arrangement of the lymph 

 nodes, Job ('22) reports as follows: 



There is a definite plan in the structure and arrangement of 

 the lymph nodes in the rat. 



There are two types: Type I where the nodular portion sur- 

 rounds the sinusoidal portion, except at the hilus; and type II 

 where the nodular and sinusoidal portions are lodged at op- 

 posite ends of the node. 



In type I, where the nodular portion covers the whole of the 

 node, except at the hilus, a peripheral sinus is present over the 

 whole of the node; but in type II the peripheral sinus is present 

 only over the nodular division. 



A collateral circulation, that is, lymph vessels passing from 

 the peripheral sinus over the surface of the node to the efferent 

 vessels at the hilus, is a normal, constant structure in type II 

 nodes. 



Accessory nodes, which are the result of some special stimulus, 

 are always type I in structure. 



Frey's suggestion, that the sinusoidal feature of the node 

 structure belongs more properly to the visceral areas, is further 

 supported. 



As to topographical arrangement, number and type, the 

 lymph nodes of the rat are as constant as the other organs of 

 the body, table 42. 



