ced in number (aplasia). The capillaries 

 are enomiously dilated and full of red 

 blood corpuscles but in a discontinuous 

 way. 



Under a strong power the scarceness, 

 reserabling disappearance of the poly- 

 morphonuclear leucocytes is made evi- 

 dent. 



The myelocytes, which are consi- 

 derably less numerous than in normal 

 bone-marrow show pronounced regres- 

 sive changes; the nucleus of many is 

 pyknotic. 



Some myelocytes make up isolated 

 groups of 3 or 4 amphophil myelocytes; 

 these are small foci of multiplication of 

 myelocytes. These groups are rarely seen. 

 The regressive changes of the myelocytes 

 are prevalent. 



A relative abundance of small cells 

 with the appearance of Ij-mphocytes may 

 be noticed. i 



Some fat-cells have their normal di- 

 mensions; almost all, however, are re- 

 duced in volume; the nucleus is swollen 

 and its finer structure more evident than 

 usual, being readily stained by hœmato- 

 xylin. In the protoplasm appears a zone 

 where the structure is clearly reticular. 

 This zone is foimd immediately round 

 the nucleus, which occupies a much 

 more central position than in fat-cells 

 from normal bone-marrow. 



The megalocaryocytes found are the 

 seat of pronounced regressive changes 

 (plasma more or less intensely stained 

 by eosin, nucleus in frank caryolysis). 



Round the degenerating megaloca- 

 ryocj'tes are found frequently cells with 

 the appearance of lymphocytes, but not 

 plentifully; in the protoplasm of the 

 megalocaryocytes, remains of phagocy- 

 ted cells. 



In the bone-marrow of rabbit 210 

 which died not quite 17 hours after the 

 commencement of immimisation, lhe le- 

 gions are as follows: 



Lesions of the vessels; pronounced 

 congestion of blood spaces. 



Tesions of reticulum: pronounced 

 œdema. 



Lesions of parenchyma cells: 



1) pronounced reduction in number 

 of bone-marrowcells (aplasia). 



2) almost entire disappearance of 

 pobjmorphonnclear Jeiwocj/tes. 



3) pronounced ref/ressive ctxanges in 

 myelocijtes and megaIocanjoci;tes, 



i) reproduction of amphophil mye- 

 locytes which constitute little groups of 

 3-4- cells; these foci are sparse and relati- 

 vely rare. 



5) reduction in number of the fat- 

 c:'lls, which show a nucleus with the 

 finer structural details clearer than 

 under normal conditions. This nucleus 

 is displaced towards the centre of the 

 cells and the protoplasm around it hag 

 a ixry evident reticular structure. 



6) relative abundance of cells mor- 

 phologically identical to lymphocijtes. 

 (diffuse infiltration of lymphocytes). 



24 hours of immunisation. 



Rabbit 212— Weight I 300 grs. 



Inoculated on April 7th 1920 at 3.30 p. tu. in mar- 

 ginal vein of ear with 1 cc. of a killed emulsion of S, 

 paratyphi A. (Emulsion A). Died after 9.00 a. m. on 

 April 8 th 1920. Antopsied before 1.00 p. m. 



Autopsy.— The bone-marrow is of a 

 dark red colour; small points of a darker 

 red may be seen in it. 



Its consistence is slightly diminis- 

 hed. The surface is shiny. 



The central vein is voluminous, tuty 

 gid, looking like a cord of red colour, 

 easily separated from the parenchyma 

 of the bone-marrow. 



Histologic Study. — Under a weak 

 power the bone-marrow ¡shows an evi- 

 dent reduction in the number of thti 

 parenchyma cells (Fig. 3, Plate 19). 



The reticulmn is the seat of a pro- 

 nounced, generalised cedema (Fig. 4, Pla- 

 te 19). 



The capillaries are dilated and fil- 

 led with red blood corpuscles (Fig. 3^ 

 Plate 19} between which normoblaslfl^ 



