The quantity of virus recovered from neoplastic tissues is dependent in part on: (1) the concentration of the agent in the source tissues and (2) the techniques used to extract the virus.

To determine which of the three most grossly affected organs, i.e., liver, spleen, and lymph nodes, would yield the greatest amount of leukemia virus, a series of 3 experiments was carried out. Leukemic livers, spleens, and lymph nodes (peripheral and mesenteric) were removed and pooled separately from BALB/c mice approximately 8 weeks after inoculation of the leukemia virus. The tissues were tested as individual sources of the leukemia agent. The method of virus extraction and recovery was that described in procedure A. The resulting particulate fractions were diluted in serial tenfold steps in 0.05 m pH 6.8 sodium citrate buffer containing 1.0 mg. percent of hyaluronidase. BALB/c mice less than 36 hours of age were inoculated subcutaneously with 0.1 ml. of the respective dilutions.

Analysis of the biological response data (percentage incidence and time-to-death with leukemia) suggested a relatively low concentration of the virus in the liver tissues. In addition there was a greater variability of the individual animal responses within the dose groups. No difference in the quantity of extractable virus between spleens and lymph nodes was indicated by the data.

Results of the experiment with leukemic lymph nodes as virus source material are presented in table 1. From the high percentage incidence (column 3) and the low average latent period (column 4) values, it is seen that these tissues serve as excellent source materials of the leukemia virus. Further, it is indicated that the procedure used to extract the virus is of value in the recovery and concentration of the biologically active principle from the source tissues.

Table 1. Titration Of Virus Concentrate Prepared From Leukemic Lymph Nodes

Log dilution

Number positive

Number inoculated

Incidence (percent)

Average latent period* (months)

10^0

19/19

100

2.9

10^-1

46/46

100

3.0

10^-2

43/43

100

3.4

10^-3

37/37

100

4.0

10^-4

39/39

100

4.5

*Average time-to-death with leukemia after virus inoculation. All inoculated mice died of leukemia by the 7th month.