THE BLOOD OF CHICK EMBRYOS
217
granulocytes is divided by 100. For the hen, the neutrophil index was
estimated to be 2·24 and the eosinophil index 2-13. Changes in this index
in chick embryo neutrophils from the 6th day and in eosinophils from
the 15th day are shown in Fig. 4. The values for eosinphils are lower and
in proportion to their later appearance in circulation. It is apparent that
there is a gradual maturation in both lines with the exception of a short
period towards the end of incubation (shown by the fall in the index
curve, Fig. 4), when a rapid increase in the number of leucocytes per
cu.mm takes place. The prolymphocytes and promonocytes mature as
mentioned above. Among the prolymphocytes, small forms, up to 6 μ
in diameter, appear first then medium-sized forms (9/x) appear from
the 14th day, and lastly large ones appear (11-12 μ) on the 15th day. At
hatching they are in the proportion of 8%, 79%, and 13%, respectively,
and in the adult hen 13-0%, 74-5%, and 12-5%.
2. Leucocyte Number per cu.mm
Studies concerned with leucocyte number in chick embryos are rare.
The reason is clear. Though various solutions were recommended for
counting leucocytes by the same method as erythrocytes (Blain, 1928;
Hirschfeld and Hoitink, 1937; Wetmore, 1940; Darcel, 1951; Hairston,
1955; Denington and Lucas, 1955; Dixon and Torberta, 1959) the only
more or less reliable method is to relate the relative number of white and
red blood cells in smears to the erythrocyte number per cu.mm. A
complete study of the number of all white blood cell types per cu.mm
was undertaken by Lemez (1955) from the first appearance of neutrophils
in the circulation on the 4th day until the 1st postembryonic day (Fig. 4).
The relative number of leucocytes to 50,000 erythrocytes was estimated
in each of 12 embryos every incubation day.
In respect of the leucocyte number, three periods could be distinguished; first, from the 4th till the 13th day, when the number steadily
increased up to about 1000 per cu. mm; second, from the 14th till the
17th day when the average number was about 3000 ; and third, from the
18th day till the 1st postembryonic day during which there were about
10,000 leucocytes per cu.mm on the average (Fig. 4). According to
Kelly and Dearstyne (1935) and Blount (1939a) the number of leucocytes
of all kinds is rarely over 10,000 on the 1st day after hatching, which is
somewhat lower than our value. On the other hand, the data of Burmester
et al. (1941) agree very well with ours in the last few days of incubation
(Fig. 4). Weiler and Schechtman (1949) reported that, between the 14th
and 16th day of development, 100-150 granulocytes and about 1000
lymphocytes were present in a microlitre of blood. The former number
seems to be extremely low and the latter extremely high compared with
values given by other authors. The data on granulocytes given by
217
granulocytes is divided by 100. For the hen, the neutrophil index was
estimated to be 2·24 and the eosinophil index 2-13. Changes in this index
in chick embryo neutrophils from the 6th day and in eosinophils from
the 15th day are shown in Fig. 4. The values for eosinphils are lower and
in proportion to their later appearance in circulation. It is apparent that
there is a gradual maturation in both lines with the exception of a short
period towards the end of incubation (shown by the fall in the index
curve, Fig. 4), when a rapid increase in the number of leucocytes per
cu.mm takes place. The prolymphocytes and promonocytes mature as
mentioned above. Among the prolymphocytes, small forms, up to 6 μ
in diameter, appear first then medium-sized forms (9/x) appear from
the 14th day, and lastly large ones appear (11-12 μ) on the 15th day. At
hatching they are in the proportion of 8%, 79%, and 13%, respectively,
and in the adult hen 13-0%, 74-5%, and 12-5%.
2. Leucocyte Number per cu.mm
Studies concerned with leucocyte number in chick embryos are rare.
The reason is clear. Though various solutions were recommended for
counting leucocytes by the same method as erythrocytes (Blain, 1928;
Hirschfeld and Hoitink, 1937; Wetmore, 1940; Darcel, 1951; Hairston,
1955; Denington and Lucas, 1955; Dixon and Torberta, 1959) the only
more or less reliable method is to relate the relative number of white and
red blood cells in smears to the erythrocyte number per cu.mm. A
complete study of the number of all white blood cell types per cu.mm
was undertaken by Lemez (1955) from the first appearance of neutrophils
in the circulation on the 4th day until the 1st postembryonic day (Fig. 4).
The relative number of leucocytes to 50,000 erythrocytes was estimated
in each of 12 embryos every incubation day.
In respect of the leucocyte number, three periods could be distinguished; first, from the 4th till the 13th day, when the number steadily
increased up to about 1000 per cu. mm; second, from the 14th till the
17th day when the average number was about 3000 ; and third, from the
18th day till the 1st postembryonic day during which there were about
10,000 leucocytes per cu.mm on the average (Fig. 4). According to
Kelly and Dearstyne (1935) and Blount (1939a) the number of leucocytes
of all kinds is rarely over 10,000 on the 1st day after hatching, which is
somewhat lower than our value. On the other hand, the data of Burmester
et al. (1941) agree very well with ours in the last few days of incubation
(Fig. 4). Weiler and Schechtman (1949) reported that, between the 14th
and 16th day of development, 100-150 granulocytes and about 1000
lymphocytes were present in a microlitre of blood. The former number
seems to be extremely low and the latter extremely high compared with
values given by other authors. The data on granulocytes given by