GASTRIC C/ECA OF THE HETEROPTERA. 12 7 



three or four hours, when incubated at 35 C., the normal serum 

 in these same dilutions gave no trace of the reaction. It showed 

 no more flocculation than regularly took place in the untreated 

 checks, although there does often appear to be a slight reaction 

 in dilutions as high as 1-20 where normal rat serum is used. 



From a careful study of the bacteria as they occur in the caeca 

 of the different Heteroptera, supplemented by the results of this 

 culture work, it seems highly probable that many, and perhaps 

 all, of the different and highly characteristic forms observed in 

 the caeca of so many of these insects are really abnormal involu- 

 tion forms of an organism presumably something like the caecal 

 bacteria of Anasa tristis. This cannot be certainly determined, 

 however, until at least a few of these peculiarly shaped organisms 

 have been cultivated beyond question. It will be remembered 

 that during the culture work with the caecal bacteria of Murganiia 

 histrionica, growth was secured from a small per cent, of the insects 

 that had been dead for some time. The organism isolated in this 

 case being a short, motile form, very similar in the morphological 

 and cultural characters recorded to the bacteria from Anasa 

 tristis. As there appeared at that time, however, no way of 

 determining positively whether these really represented the true 

 caecal organism of the cabbage bug or were merely accidental 

 invaders which had appeared after the death of the insect, the 

 cultures were all discarded, as has already been mentioned, after 

 having been studied in only a very superficial way. 



Evidently the only method available in a case such as that 

 described for Mnrgantia is the agglutination test as applied to the 

 cultures from Anasa tristis immunization with the bacteria of 

 the particular insect studied, direct from the caeca, and testing 

 the resulting serum against any doubtful cultures obtained from 

 these organs. 



I have had no opportunity as yet to repeat this work with 

 Murgantia, but expect eventually to make a careful comparative 

 study of the caecal organisms from a number of host species, 

 concentrating especially on such forms as Murgantia, Peribalus 

 limbolarius, Peliopelta abbreviata, or others in which the normal 

 organism is equally characteristic; the agglutination test, of 

 course, being used as a basis for the work. 



