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Consecutive weekly observations on the total white cell count of the peripheral blood were made on 5 groups of normal rabbits, a total of 45 animals, during a period of 20 months from October, 1927 to July, 1929. The duration of individual group examinations varied from 8 to 35 weeks. In the case of 4 groups followed 13 to 35 weeks, the general trend of the total white cell means was toward increasing values; with the group followed 8 weeks, the means were maintained at a constant level. The changes in the levels of the granular cell means were usually accompanied by changes in a similar direction of the non-granular cell means. In the case of 3 of the 4 groups followed for the longest periods, the greatest relative alterations occurred in the non-granular cells. The fluctuations in the mean values of the total white cells and of the granular and the non-granular cells which were observed in one group of rabbits, were also generally observed in another group examined during the same months. The period of greatest irregularity in the mean values of the total white cell means and of the granular and the non-granular cell means as well, occurred during the late winter and spring months of both years. The general level of the total white cell mean values in the groups examined during 1927-28 was higher than that of the groups observed during 1928-29. A similar difference was found in the granular and non-granular mean values but it was somewhat less marked in the case of the granular cells.

1. Repeated platelet counts, 991 in number, were made on 148 adult male rabbits of various breeds and types which were specifically selected on the basis of physical fitness and continued freedom from disease. The observations extended over a 2(1/2) year period (1929-32). 2. A unimodal, peaked, moderately asymmetrical distribution curve was obtained and an analysis of the results gave the following values: the mean, 532,645 platelets per c.mm.; the median, 520,604 per c.mm.; the mode, 503,962 platelets per c.mm. respectively. 3. The extent of the variation among the counts is shown by the standard deviation of 124,960. High platelet counts were found to occur more frequently than low counts, a result that is reflected in a significant skew to the right in the frequency curve. 4. It was calculated that in healthy male rabbits a platelet count of less than 220,000 or more than 845,000 per c.mm. should be considered abnormal.

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.

A study of the red blood cells, hemoglobin, blood platelets, and the total and individual white blood cells was made on 180 male rabbits of known age and representing fifteen standard breeds. An attempt was made to eliminate or bold constant such variables as age, sex, season, time of examination, technical errors, food, housing, and disease. The mean, variance of the mean, and standard deviation were calculated for each breed sample and for the group as a whole. An analysis of the variance showed that the variation between the breed samples was significantly greater than the variation within the breed samples for the red blood cells, hemoglobin, blood platelets, total white blood cells, basophiles, eosinophiles, and lymphocytes per cubic millimeter and in per cent and the neutrophiles in per cent. No significant variations were detected in the monocytes except when the breeds were divided into heavy and light breeds. No variation in the neutrophiles per cubic millimeter was detected; a large number of the breeds had exactly the same mean neutrophile level. Characteristic blood formulae were found for the various breed samples having an adequate numerical representation. It was concluded that the varying blood formulae could not be explained on any other, except an hereditary (genetic) basis.

Consecutive weekly observations on the neutrophile, the basophile, and the eosinophile counts of the peripheral blood were made on 5 groups of normal rabbits, a total of 45 animals, during a period of 20 months from October, 1927 to July, 1929. Individual groups were examined 8 to 35 weeks. In the case of the 4 groups followed 13 to 35 weeks, the general trend of the neutrophile cells was towards increased mean values; with the group followed 8 weeks, decreasing values were found. An increase in the mean values of the basophile cells was observed in the two groups of rabbits followed in 1927-28; in the groups of 1928-29, the mean values decreased. The mean values of the eosinophile cells showed no definite trends but the findings were characterized by abrupt and marked fluctuations. The periods of greatest irregularity in mean neutrophile and eosinophile values occurred in the fall and the late winter and spring months of both years, but in the case of the basophiles, the irregularities were distributed throughout the first year and occurred chiefly in the winter months of the second year. The major trends and many of the minor fluctuations as well which were observed in the mean cell values of one group of rabbits were also generally seen in another group examined during the same months. The general levels of the neutrophile, the basophile, and the eosinophile mean values in the groups examined during 1927-28 were higher than in the groups of 1928-29.

Successive blood counts at weekly intervals were made on rabbits inoculated with a transplantable malignant neoplasm of epithelial origin. There were 78 animals distributed in 9 groups; the period of observation after inoculation was 2 months. The results have been considered with respect to the character of the tumor process as determined by postmortem examination, the animals being classified as deaths, probable deaths, probable recoveries, and recoveries. The blood findings have been analyzed on the basis of the values derived from normal rabbits. A comparison has also been made with the results of preinoculation counts. In rabbits in which the tumor process was of pronounced or well marked severity, the numbers of monocytes became greatly increased; the neutrophiles and the total white blood cells were also increased; the eosinophiles, and to a less extent, the basophiles and lymphocytes were decreased; the red cell count was decreased and the hemoglobin content was lowered. In rabbits which recovered from the tumor inoculation, there were no outstanding changes in the blood picture when the findings for the entire observation period were considered. In the group of probable recoveries, the results were variable; there was, however, a definite although moderate increase of monocytes, and in general, the findings reflected the mildness of the disease when compared with those of the fatal cases and the group of probable deaths.