148 
Spirochaetae and Acanthia 
Conclusions (I). 
The foregoing experiments show that Spirochaeta duttoni retains 
its virulence after a sojourn of 5 or more days in the intestine of 
Acanthia lectularia when the insect is maintained at a temperature of 
12 D C. Living (motile) spirochaetes were observed in the gut-contents 
of the bugs up to 6 days at 12°C. but only up to 6 hours at 20—24° C. 
The observations made at various temperatures appear to indicate that 
the spirochaetes are simply digested by the bug and that their more 
rapid disappearance from the insect’s gut at higher temperatures is 
dependent upon the insect’s digesting its food more rapidly when kept 
warm. The disintegration of the ingested red blood corpuscles in the 
insect’s gut runs parallel to that of the spirochaetes, though the latter 
can be found in stained specimens long after the corpuscles have 
disappeared and the spirochaetes themselves have ceased to give any 
evidence of life. 
Typical longitudinally dividing forms were encountered in stained 
preparation made from the contents of the bug’s intestine 3^ to 8^ hrs. 
after the bug had fed on spirochaete blood, when the insects were 
maintained at 24° and 20° C. respectively. 
The rapid death of the spirochaetes in bugs maintained at 20—24° C. 
may account for the negative results of the infection experiments 
carried out by Breinl, Kinghorn and Todd. Although the bug is not 
the true host of Sp. duttoni it is conceivable that it may serve as a 
mechanical carrier of the parasite. It has been proved that different 
species of Ti'ypanosomes may be transferred by means of the bites of 
blood-sucking flies ( Glossina, Stomoxys 1 2 ) and that the plague bacillus 
may be transferred by means of Acanthia lectularia 2 when only a 
short interval (some minutes or usually less than 24 hours) elapses 
between the successive bites of the insect. Such experiments still 
require to be carried out with the bug and pathogenic spirochaetes. 
Incidentally I may add that prior to accidentally losing the strain of 
Sp. duttoni it was maintained with undiminished virulence by passage 
through 100 mice during the course of one year. 
I am indebted to Dr Levaditi of the Pasteur Institute for the strain 
of Sp. duttoni (R. Koch’s) Avith which these experiments were carried 
1 See Nuttall (1907), for a summary of this subject. 
2 See Verjbitski (1908) in the references which follow. 
