40 Psyche [June 



impression that I depreciate the importance of these cells. How- 

 ever, even during metamorphosis their action is not conjfined 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 amsebocytes, 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 tliat 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 microorganisms, supposedly pathogenic, 

 were introduced. For example: Ten mature female grasshoppers 

 (Melanoplus femur-rubrum) were each injected with Vio 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 §, 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 



