Immunity of Rats towards Jensen^ s Rat Sarcoma. 17 



Material was obtained in the following manner : Rats were inoculated 

 with miiLced tumour into both axillae. After varying lengths of time, one 

 graft was removed by operation for histological examination ; the other was 

 allowed to remain in order to indicate, by its growth, the degree of suscepti- 

 bility of the rat. The amount inoculated was 0"05 c.c. The appearances 

 when minute fragments were used were found to be exactly similar to those 

 when 0"05 c.c. was inoculated ; in each case the centre of the inoculated mass 

 quickly degenerated, so that, by the second or third day, only cell-debris 

 remained ; only the outer surface of the inoculated material for a depth of a 

 few cells remained viable. 



Material was fixed in Gilson or Carnoy solution, and stained as a routine 

 with pyronine-methyl green ; other methods were also occasionally used, 

 dilute haematoxylene (1 in 100 long process), polychrome methylene blue, 

 and azurin 2. 



Before describing the microscopic appearances of the grafts, it is necessary 

 to discuss the nomenclature here used with reference to the cells which are 

 found in the connective tissue and reaction tissues of the rat. There can be 

 no confusion about the following cells: fibroblasts, fat cells, mast cells, 

 plasma cells (plasmoidocytes), and polymorphonuclear leucocytes. There 

 remains a polymorphic group of cells, the lymphocytes (polyblasts of 

 Maximow), which have been classified according to their histogenic, hsemato- 

 genic, or endothelial origin, and also according to their characters and 

 functions into adventitial cells, wandering cells, macrophages, clasmatocytes, 

 small amoeboid wandering cells, large and small mononuclear cells. Since 

 they appear to grade one into the other as regards both their origin, function, 

 and characters, the term lymphocyte will be here used for the whole group. 



1. The Microscopic Appearances of Sichctitaneous Grafts in Susceptible Animals. 



(a) Tlie Appearance 24 Hours after Inoculation. — The fatty areolar con- 

 nective tissue around the inoculated sarcoma emulsion is seen to be distended 

 with a structureless exudate for a distance of from 2 to 4 mm. It is 

 separated from the emulsion by a narrow space or cleft which is often partly 

 filled with collections of polymorphonuclear leucocytes. The groundwork of 

 this reaction tissue consists of oval or round masses (diameter 0'06-0"08 mm.) 

 of hyaline material separated by bands of fine connective tissue fibres. 

 Sparsely scattered over this groundwork, and confined chiefly to the bands 

 between the hyaline masses, are cells of several different kinds (see fig. 12). 

 Close to the emulsion are many polymorphonuclear leucocytes, and imme- 

 diately outside the crack a few healthy sarcoma cells. At the periphery a 

 small number of mast cells and small fibroblasts are to be seen, as well as fat 



VOL. xc. — B. 



