196 L. R. CLEVELAND. 



periments is that the thermal death point of the protozoa is 

 3-4 C. lower than that of the insect host. 1 



After incubation the termites were closely observed to note if 

 they at any time became abnormal; to prevent the growth of 

 moulds in the jars, for moulds are very destructive to termites; 

 to be certain that the jars contained neither too much nor too 

 little moisture a thing that can only be learned from long ex- 

 perience in keeping large numbers of termites in captivity and an 

 intimate knowledge of their habits in nature. Every known pre- 

 caution was used to keep the termites during incubation in ex- 

 actly the same environment, except temperature, as the unincu- 

 bated controls. After incubation the incubated and the unin- 

 cubated termites were kept under identical conditions, as re- 

 gards food, temperature, moisture, light, etc. 



The termites become abnormal in from five to fifteen days 

 after they have been removed from the incubator. They are less 

 active and their abdomens, if carefully examined, may be seen to 

 be smaller and slightly flattened. The length of time required 

 for abnormalities to appear depends no the kind of wood fed 

 after incubation, the more decayed the wood the longer it is 

 before any abnormalities appear. In two to five days after this 

 first symptom is noticed the abdomen becomes still more flattened. 

 Soon it is very much smaller and almost flat, and two or three 

 days later the animal can scarcely be made to move at all, for 

 only a modicum of vitality remains. Death occurs, on the aver- 

 rage, from 10-20 days after incubation. It occurs, as shown in 

 Table II., in some instances in less than ten days and in a few 

 cases after twenty days, the longest being 27 days. In the less- 

 decayed wood, as mentioned above, death occurred early, and 

 in the most decayed, it occurred late. But why did it occur at all? 

 Why did the incubated termites die? 



The death of the incubated termites sterile, uninfected, 

 uninfested and defaunated, so far as protozoa are concerned- 

 may be due to the change in temperature, i.e., the incubation 

 per se; it may be due to the killing off of all the intestinal pro- 

 tozoa; or it may be due to the killing of intestinal bacteria and 



1 Termopsis sp. from Ashland, Oregon, is killed at a lower temperature. It is 

 killed in less than 24 hours at a temperature of 35.5 degrees C. Work on the T. D. P. 

 of termites from various parts of the world is now in progress and the results will be 

 published in a later paper. 



