1917] Glaser—Growth of Insect Blood Cells in Vitro 5 
syncytia. Ihave frequently given up slides as hopeless on account 
of what seemed to me to be complete disintegration, yet on reéxam- 
ination in about two weeks, I was astonished to find clusters of heal- 
thy looking, growing cells. 
I have kept true army and fall-army worm blood preparations 
alive for one month without washing out the cultures or transferring 
them to a fresh medium. Gipsy-moth blood cultures have been 
kept alive for as long as seventeen weeks without washing or trans- 
ferring. It is true, the cells were no longer vigorous and showed 
signs of beginning degeneracy, but they were alive. After washing 
out these old cultures with sterile Locke’s solution and filter paper, 
as is usually done, and transferring to a fresh medium like Locke’s 
solution the cells grew and multiplied as before. 
In so far as the morphological elements contained in insect blood 
are concerned, the ordinary amcebocytes (PI. I, figs. 3 and 4) are 
the only ones which multiply in tissue cultures. The minute 
amcebocytes (PI. I, fig. 5), the mulberry corpuscles (PI. I, fig. 2), 
and the cytoplasmic free cells (Pl. I, fig. 6) described by me in 
1915! always disintegrate. A difference of opinion seems to exist 
in the literature as to the origin of the blood corpuscles of larval 
and adult insects. From my studies it appears that the blood 
cells, after their differentiation from the mesoderm during em- 
bryological development, simply maintain their numerical equilib- 
rium in larvee and adults by dividing mitotically at certain inter- 
vals. I cannot find any so-called blood corpuscle forming tissue 
at least in sections of caterpillars. 
Some of the visible changes observed on the culture slides in 
normal degenerating blood cells have proved instructive and have 
further helped to strengthen my views (published elsewhere) in 
regard to the nature of the polyhedral bodies found in the nuclei 
of certain pathological cells. Normal disintegration of insect 
blood cells is always accompanied by the formation of protein 
crystals within their cytoplasm. Crystalline disintegration ac- 
companied by granular disintegration seems to be the rule in nor- 
mal disintegrating insect tissue. Granular disintegration alone 
seems to be exceptional in blood cells at least. In the polyhedral 
diseases of insects protein crystals are likewise formed within the 
1 Wilt of gipsy-moth caterpillars. Journal of Agricultural Research. Vol. IV, No. 2, May, 
1915, p. 113. 
