Teco Wn ong ge 
VOL. XXV JUNE, 1918 No. 3 
ON THE EXISTENCE OF IMMUNITY PRINCIPLES IN 
INSECTS. 
By R. W. Guaser. 
During the course of my work on various diseases of insects, I 
have often been confronted by results which seemed to point 
towards the existence of immunity principles. I failed to become 
convinced, however, till I instituted a series of experiments meant 
to prove or disprove my views. Other workers, also, on investigat- 
ing caterpillar and grasshopper diseases, have been unable to ex- 
plain some of their results without assuming the possibility of 
physiological immunity, but direct proof for their contentions has 
been lacking. 
In physiological work of this sort it is very difficult to obtain 
quantitative data for the reason that the amount of blood obtain- 
able from a particular insect amounts to only one-tenth to one-fifth 
of a cubic centimeter. In one series of experiments I managed to 
obtain quantitative results. The other data are qualitative but, 
I hope, no less important. 
THE QUESTION oF PHAGOCYTOSIS. 
Since all entomological text-books emphasize the importance of 
the blood cells in ridding the insect body from the invasion of 
foreign substances this question was first investigated. In prac- 
tically all the literature on the subject, insect blood cells are com- 
pared with the mammalian white blood corpuscles. An exceed- 
ingly aggressive nature is attributed to them and their movements 
are described as actively ameboid, engulfing foreign substances 
with great avidity. I was greatly astonished to find that this view 
was incorrect and that the blood cells are visibly rather passive. 
Of course, we know that the so-called amzebocytes play an impor- 
tant réle during metamorphosis, and I do not wish to create the 
1 Contribution from the U. 8. Bureau of Entomology in codperation with the Bussey Insti- 
tution of Harvard University. (Bussey Institution, No. 143.) 
