1918] Glaser — On the Existence of Immunity Principles in Insects 43 



motionless. The blood cells showed cell division and the forma- 

 tion of the tissue-like, syncytial masses. Bacteria were not found 

 within the cytoplasm of any of the cells. In two weeks the two 

 culture slides presented much the same condition with the excep- 

 tion of the blood cell syncytia which were much larger. The 

 observations were discontinued after two weeks. 



The foregoing experiments were repeated with army worm and 

 gipsy moth caterpillar blood. The results were in perfect harmony 

 with the grasshopper blood observations. 



From the tissue culture work, we are forced to conclude that in a 

 mixture of insect blood cells and bacteria, the blood cells are not 

 the visible aggressors. However, the blood seems to be able to 

 overcome bacterial invasion to a certain extent. Substances are 

 elaborated which antagonize the bacteria. On the culture slides, 

 the quantity of the blood is not sufficient, and metabolism is low- 

 ered, so that antagonistic substances are not formed so rapidly 

 nor so abundantly as is the case within the body of the insect. 

 For this reason, although the bacteria were rendered ineffective on 

 the culture slides and permitted the blood cells to grow, they were 

 not killed. All of these questions will be more clearly elaborated 

 in the next section. 



Extracellular Antagonistic Substances. 



In a large series of experiments with grasshoppers {Melanoplus 

 femur-rubrum) and Bacillus poncei four animals remained alive 

 after two weeks. These animals, like the remainder, which died, 

 had been injected with Vio of a cubic centimeter of a 24 hour bouillon 

 culture of B. poncei. I suspected that these four animals were im- 

 mune and thought it might be possible to demonstrate the exis- 

 tence of some immunity principle, such as an agglutinin. Of 

 course, on account of the small amount of blood obtainable 

 from a grasshopper, it is extremely difficult to perform a Widal 

 test with all the high dilutions, but I am confident that my experi- 

 ments are significant in spite of this shortcoming. 



Four depression slides were prepared from the four supposedly 

 immune animals. A leg from each grasshopper was broken and a 

 drop of blood from each was caught on a separate sterile cover- 

 slip. To each cover-slip I added one platinum loop-fuU of a 24 

 hour bouillon culture of B. poncei. The culture was first examined 



