1. The blood cytology of 91 rabbits was studied prior to inoculation with a transplantable malignant neoplasm. The following statements refer in each instance to the mean values of the pre-inoculation counts.

2. The animals which were most resistant to the malignant disease had, before inoculation, normal red and white cell counts, normal hemoglobin percentages, high eosinophile counts, and low counts of monocytes and lymphocytes. The relations of the neutrophile and basophile counts were irregular, but normal values also appeared to be associated with greater resistance.

3. The most susceptible animals were those which had, before inoculation, red cell counts above 5,500,000 or below 5,000,000 per c.mm.; hemoglobin above 70 per cent or below 60 per cent (Newcomer); white cell counts below 6,000 or above 8,500 per c.mm.; low eosinophile, high monocyte, or high lymphocyte counts.

4. No animal with any of the following findings prior to inoculation recovered completely from the tumor as determined by autopsy examination: red cells above 5,500,000 per c.mm. of blood; hemoglobin above 70 per cent; total white cells above 10,000 per c.mm.; eosinophiles below 120 per c.mm., or below the relative value of 1.5 per cent; basophiles below 400 per c.mm., or below the relative value of 6 per cent; lymphocytes above 3,600 per c.mm.; monocytes above 1,500 per c.mm.; neutrophiles above 5,000 per c.mm.; and total granular cells above 5,700 per c.mm.

In the case of each of the following pre-inoculation values, only 1 animal was completely free from tumor at autopsy: hemoglobin below 60 per cent; red cells below 4,800,000 per c.mm.; total granular cells below 3,300 per c.mm.; total non-granular cells below 2,300 per c.mm.; total non-granular cells above 3,700 per c.mm. No animal with pre-inoculation eosinophiles above 3.9 per cent, or basophiles above 16 per cent died from the tumor.

5. The blood findings before inoculation could be related to the character and outcome of the malignant disease, from the standpoint of animal groups as well as in the case of individual rabbits.

6. From the results of the experiments here reported, it seems possible to predict with an accuracy of between 80 and 90 per cent the individual resistance or susceptibility of rabbits to the tumor by a study of their blood cells before inoculation.

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