4frrc either found in the interior of the 

 blood spaces or else are in the reticulum 

 where they appear as isolated elements. 



3) reduction in number, almost ab- 

 sence, of polymorphonuclear leucocytes. 



4^ regressive changes in the myelo- 

 cytes, megalocaryocytes and fat-cells. 



5) proliferation of myelocytes, with 

 not infrequent disseminated foci, ma- 

 de, up of 4 or more of these cells. 



Probable interpretations. 



The lesions seen in the bone-marrow 

 of rabbits 210 and 212, which died res- 

 pectively 17 and 20 hours after the 

 beginning of immunisation, are of the 

 same nature. 



Small variations of intensity of 

 the lesion, only, are to be seen. 



Thus in rabbit 210, the œdema of 

 the reticulum is more accentuated than 

 in 212. In rabbit 212 the cells with 

 the appearance of lymphocytes are 

 still more numerous and diffusely distri- 

 buted than in rabbit 210. 



These lesions are probably due to- 

 the following: 



The conspicuous reduction in leu- 

 cocytes is to be explained, naturally by 

 the leucocytosis observed in this phase 

 of immunisation. 



The multiplication or regeneration 

 of the myelocytes is due to this same 

 leucocytosis. 



The congestion of the capillaries ap.d 

 «edema of the reticulum are directly 

 dependant on the introducticE into the 

 circulation of the antigen (dead bacte- 

 ria), certainly bringing with it toxins 

 (endotoxins). The congestion must pre- 

 cede the cedema which is only the con- 

 sequence of an intense and lasting con- 

 gestion. We had, besides, the opportu- 

 nity to see the ease with which, in va- 

 rious pathological conditions, the œde- 

 ma of the reticulum of the bone-marrow 

 produces itself, and which is explained 

 by the special structure of the capilla- 

 iTies of the bone-marrow. 



As to the regressive changes seen 



in the myelocytes, megalocaryoc\'tes ami 

 fat-cells, I think that the vascular le- 

 sions (œdema and congestion), bringing 

 with them modifications in the cellular 

 metabolism, are in themselves sufficient 

 explanation; it is not possible, however, 

 to exclude even here an action of the 

 antigen. 



The explanation of the abundance 

 of cells with the morphology of lympho- 

 cytes offers some difficulty; the same 

 fact had already been observed by 

 SEI-LING in the regeneration of bone- 

 marrow after benzol intoxication; it is 

 most probable that it should be a case 

 of emigration of these cells from capilla- 

 ries of the bone-marrow where they are 

 also to be seen in the sections (Fig. 4, 

 Plate 19). 



36 hours of Immunisation. 



Rabbit 21 3- Weight 1.300 grs. 



Inoculated in marginal vein of the ear with 1 cc. of 

 « killed emulsion of B. paratyphi A. (Emulsion K) at 

 3.30 p. m. on April 7 th 1920, 



Died after 9.00 a. m. on April 8 th 1920. Autopsied 

 at l.CO p. m. on same day. 



Autopsy — The bone-marrow has a 

 lightred colour. The consistence is di- 

 minished, the organ is easily dilacerated, 

 leaving pieces sticking to tlie bone- 

 when the rest is removed. I'he central 

 vessels arc not very conspicuous. 



Histologic Study—The lesions of the 

 bone-marrow of rabbit 213, died at the 

 3Gth hour of immunisation, are of the 

 same kind as those seen in rabbit 212. 



The differences are: 



1) The congestion is less pronoun- 

 ced. 



2) The proliferation of myelocyte» 

 is more pronounced, figures of indirect 

 division are frequent 



3) Cells with pigment ar© fouad in 

 greater nxmiber. 



2nd Day of immunisation. 



RabMt 2t4-Weiflit I 300 {ra. 



On April 7 th 19» at 3.30 p. m. , Inonteted ts twt 



