GASTRIC CMC A OF THE HETEROPTERA. 123 



a few days after the first appearance of growth, however, forms 

 were observed in many of the tubes which were clearly not of 

 this type. In about a week the two abnormal forms which had 

 appeared in the preceding experiment were observed in a number 

 of these tubes; and, in addition to these, a third type was also 

 discovered which appeared in several of the tubes as a very 

 large, oval, yeast-like organism often over 4 microns long by 

 2-3 microns wide. 



As all contamination from without had been excluded beyond 

 question, all of these unusual forms must, certainly have come 

 from the caeca; and as nothing resembling any of them had ever 

 been observed in these organs by direct examination, their 

 appearance in the cultures was very difficult to explain. 



Upon close examination it was seen that these contaminating 

 organisms were not strictly constant in form, although it did 

 not seem possible at first that these strikingly different organisms 

 could be involution forms of the bacillus that first appeared in 

 cultures from the caeca. The yeast-like bodies were usually free, 

 with one or more small typical buds at the ends; but occasionally 

 one or more of these large bodies could be seen in the long chains 

 of small coccus-like forms; and the large bacillus was not always 

 a typical rod, but very often tapered at the ends very decidedly, 

 and even merged into bodies that resembled the yeast-like forms. 

 Since it seemed possible that some of the contaminating organisms 

 were merely involution forms, and not independent organisms, 

 as had been assumed at first, it seemed worth while to make a 

 thorough study of the different forms occurring in the cultures 

 to determine how much normal contamination there really was 

 in the alimentary canal of these insects. Plate cultures were 

 accordingly made from some of the tubes that appeared most 

 highly contaminated, and these were searched very carefully 

 for different kinds of colonies; but so far as could be determined 

 by direct examination, the colonies were invariably all alike. 



Cultures were made from large numbers of these colonies 

 in an attempt to isolate the different contaminating organisms 

 that had appeared in the original bouillon tubes. All the sub- 

 cultures from the plates invariably developed into the short 

 form resembling the caecal bacillus; but when subcultures were 



