Immunity of Rats towards Jensen's Hat Sarcoma. 21 



vestige of them remains. The lymphocytes do not further increase in 

 numbers. Fibroblasts become more numerous, and by the sixth day form a 

 close meshwork around the graft, replacing the lymphocytes, which gradually 

 disappear. The collections of plasma cells at the periphery and near the 

 blood-vessels persist, and may even grow larger. By the sixth day the 

 reaction tissue has the appearance of an early fibrosis. 



Summary. — Compared to what occurs in susceptible animals, the reaction 

 in immune animals presents two striking differences, namely, the great 

 accumulation of lymphocytes on the second and third day and the rapid 



I 5 



Fig. 15. 

 Mt. 

 eel] 



C L 



— Shows the same structures as in fig. 12, but in an immune rat, 48 hours specimen. 

 , mast cell ; M, muscle ; BV blood-vessel ; F, fibroblast ; L, lymphocyte ; S, sarcoma 

 ; C, cleft. 



CD 



1 



3 C S 



Li 



Fig. 16. — Shows the appearances 72 hours after inoculation into the liver of an immune rat. 

 (Subcutaneous inoculation results in a similar appearance.) Li, liver ; LN, lymphoid 

 nodule. Other letters as above. 



degeneration and disappearance of the sarcoma cells external to the cleft. 

 The subsequent fibrosis and collection of plasma cells is also not to be seen 

 in susceptible animals. Apart from these differences, the early inflammatory 

 cedema and the later vascular connective tissue appear precisely similar in 

 both kinds of animals. 



The Microscopical Appearances when Inocidcttion is made into Liver and 

 Spleen. — The reaction tissue, both in the case of normal and immune 

 animals, is precisely similar in these organs to that which is produced 

 when inoculation is made into the subcutaneous fatty connective tissue ; 



