79 



nuclei and by comparison witii their 

 appearance in other rabbits, in which 

 transition types between these and typi- 

 cal fat-cells are to be found. I must call 

 attention to the resemblance of the nu- 

 cleus of these atrophied cells to those 

 of fixed connective tissue cells. 



The nucleus of fat-cells retains a 

 typical structure in spile of the mosl 

 marked alterations of the protoplasm: 

 thus, after the total loss of the fal-con- 

 tents of the protoplasm, the nucleus is 

 only slightly more tumid and rounded 

 and has left its peripheric position to 

 occupy the centre of tlie cell. The arran- 

 gement and disposition of the nuclear 

 chromatin is very similar to that of 

 fat-cells from normal bone-marrow. One 

 would be inclined to say that the impor- 

 tant modifications of the fat-contents 

 were physiological and not pathological. 

 In this bone-marrow increase in 

 number ot the fbced connective tissue 

 cells is evident; in some places (Fig. 8, 

 Plate 20), the parenchym is made up 

 of 10 to 15 cells placed side by side 

 and one belling the other. The nuclear 

 structure of these is that of the fibro- 

 blasts; the connective tissue fibrils can 

 be clearly distinguished. 



These points where many fibroblas- 

 ts place themselves side by side are not 

 verj' common, however: almost always 

 fibroblasts of characteristic appearance 

 are seen mixed with other bone-marrow 

 cells. All those who have studied normal 

 bone-marrow will be well aware of the 

 difficulty of recognising the fixed con- 

 nective tissue-cells under normal con- 

 ditions. 



Besides small cell foci wliich are the 

 foci of division of myelocytes and of 

 haemoglobin-containing cells (megaloblas- 

 ts and normoblasts) other more exten- 

 sive foci, made up of numerous den- 

 sely grouped cells and contrasting mar- 

 kedly with the neighbouring parenchyma, 

 are to be seen (Fig. 7, Plate 20). 



Under a strong power the cells which 

 make up the dense groups are seen to 

 be numerous polymorphonuclear leuco- 

 cytes: Many of these in one point, cove- 

 ring one anotlier show a pyknotic nucleus 

 and others are evidently undergoing com- 

 plete désintégration. This point gives the 

 hnpression of a small infarct (Fig. 7, 

 Plate 20). 



Among the densely grouped cells 

 indicated may be seen the characteristic 

 cells of bone-marrow parenchyma. 



Condensing the facts, the bone-mar- 

 row of this rabbit, killed 72 hrs. 20 mins. 

 after the commencement of immunisa- 

 tion, shows the following points of in- 

 terest : 



1") Regeneration of polymorphonu- 

 clear leucocytes (by intense division of 

 myelocytes) is tlie dominant feature. 



2o) Fat-contents of the fat cells are 

 noticed to have disappeared completely. 



3o) Infiltration of lymphocytes, so 

 marked in rabbits 212 and 2H, is in this 

 case very slight. 



4o) In this case hyperplasia of the 

 fixed connective tissue cells is seen for 

 the first time in this series. 



5o) Other foci besides foci of rege- 

 neration of haemoglobin-containing cells 

 (perivascular foci of megaloblasts and 

 normoblasts) are seen. 



6o) The whole process is evidently 

 belated, as compared 1o the process ob- 

 served in rabbit 150, killed 60 hours 

 afte the commencement of immunisation. 



6th. Day of Immunisation. 



Rabbit 407 -Weight 1.030 gr>. 



April 28 fh 1921—1.35 p. ni.— Leucocytes =16 750 

 (average). 



April 29 th 1921-1.30 p. m. - Leucocyte3=:10 250 per 

 mm' (average of 4 measurements). 



May 1 tl) 1921—2.00 p. m.— Leucoc)'tes=]5 800 per 

 mm' (average of 4 measurements). 



May 5 th 1921—1.40 p. ni.~Leucocytes=14 230 per 

 mm3 (average of 4 measurements^. 



May 6 th 1921—12.55 p. m.— Leucocytes^l4 350 per 

 mm3 fkverage of 4 measurements^. 



May 6 th 1921— Subcutaneous injection of 1 loopfui 

 of 2 milligrajnms of a 21 hours gélose culture of B, pa- 



