VIRUS-INDUCED MURINE LEUKAEMIAS 97 



occurred in our animals, and the result of cytological analysis is given in 

 Table II. The cell samples obtained from mice No. Ill and No. 112 were not 

 suitable for analysis — only a few cells could be studied; they are included to 

 show the time of the occurrence of leukaemia and the mitotic index in the 

 various sites. AK No. 110 had only 2 cells with 40+1 and 5 cells with less 

 then 40 chromosomes out of 56 cells analysed. 



CHROMOSOMES OF VIRUS-INDUCED LEUKAEMIAS IN C3H/Bi MICE 



Primary leukaemias 



Passage- A virus (cell-free extract from AK-leukaemic tissue) was injected 

 intraperitoneaUy into newborn C3H/Bi mice. The first leukaemia appeared 

 at 89 days after the injection of virus (No. 256 in Table III). In the mice both 

 thymus and spleen were enlarged, yet the mitotic index was low at the time 

 of sacrificing the animal. The cell population of marrow yielded 40 cells at 

 metaphase which could be analysed; 4 hypodiploid cells were observed. In 

 leukaemic mouse No. 251 the thymus was very much enlarged and out of the 

 50 cells analysed no ceUs were seen with the normal diploid number. The 

 chromosome constitution in three leukaemic mice is illustrated in Fig. 1. The 

 data obtained shows that in this AK- virus-originated leukaemia of C3H mice, 

 the frequency of heteroploid cells is much higher than in the spontaneous 

 primary leukaemia of the AK host. In C3II mice No. 251, 252 and 255, the 

 incidence was 69-6% (219 out of a total of 314); while in AK mice (Table I) 

 the frequency of heteroploid cells was 8-6%. It is particularly interesting to 

 note, that in C3H No. 251 all the 50 cells in the thymus had irregular chromo- 

 some numbers and in C3H No. 255 both lymph nodes analysed contained 

 about 80% heteroploid cells. 



Transplanted leukaemias 



Leukaemic cells of C3II mice, have been transplanted to new C3H/Bi- 

 strain mice. A cell suspension in saline was made from the thymus or spleen 

 of mice which had been injected at birth with Passage- A virus. In the 

 primary leukaemias, the number of cells with 40 + 1 or 40 -f- 2 chromosomes 

 was high as was shown in Table III. It was expected that by transplantation, 

 the deviation from normal might increase and the cell population might 

 become more heterogeneous. 



The number of cells transplanted was 1 x 10^ and leukaemia developed 

 after 12 to 16 days, killing the host. The chromosome numbers in transplanted 

 leukaemias are shown in Table IV. Two C3H mice, Nos. 205 and 206 have a 

 much wider variation than any other leukaemias described in the present 

 report. Both of these leukaemic mice were implanted from the primary 



