40 Psyche [June 
impression that I depreciate the importance of these cells. How- 
ever, even during metamorphosis their action is not confined to an 
aggressiveness manifested by movement but rather, I think, to 
an increase in the secretion of proteolytic and perhaps other en- 
zymes. These break down the larval tissues and prepare the va- 
rious proteins and other substances for assimilation by the imaginal 
disks that form the adult tissues. 
One gains the impression from text-books that the insect blood 
cells, called amzebocytes, during metamorphosis, bodily attack 
those larval tissues destined to destruction; that they swallow 
masses of such tissues, digest them and then wander over to the 
imaginal disks where they surrender the digested matter. I will 
attempt to show that insect blood cells are nor quite as aggressive, 
as we have been persuaded to suppose, and that one can stimulate 
the formation of certain substances acting extracellularly. It may 
be true that these substances are formed by the cells but, on the 
other hand, it is also possible that they are formed by the blood 
plasma or serum. After they are formed, however, they act in- 
dependently of any cellular organization. 
During 1916 and 1917 while studying certain bacteria pathogenic 
to caterpillars, and others pathogenic to grasshoppers, I had oc- 
casion to inoculate many insects with different cultures. In some 
of my experiments several of the insects lived in spite of the fact 
that enormous numbers of microdrganisms, supposedly pathogenic, 
were introduced. For example: Ten mature female grasshoppers 
(Melanoplus femur-rubrum) were each injected with 1/1 c.c. of a 24 
hour bouillon culture of Bacillus poncei Glaser. B. poncei is a 
highly motile organism which I obtained from the Honduran gov- 
ernment in 1915. The bacterium is ordinarily pathogenic to M. 
femur-rubrum. After intervals of 4, 1, 2, and 24 hours the animals 
were killed and a large metathoracic leg removed from each by 
breaking the joint between the trochanter and femur. The blood 
that oozed from each animal was caught on a separate sterile 
cover-slip. Some of these preparations were fixed by passing 
through a Bunsen flame, others were immersed in 70 per cent. 
alcohol, while still others were fixed with Schaudin’s corrosive 
sublimate solution. After fixation, the preparations were dried 
and stained with methylene blue. Excessive staining can be 
remedied, of course, by treatment with alcohol. After mounting 
