x MODES OF DESTRUCTION OF B. PESTIS 289 



after 1 hour's exposure, 3 loops of the medicated fluid being added 

 to each agar and broth tube. 

 The result was this : — 



a. After 1 5 minutes : on agar 1 colony of streptococci ; broth 

 slightly turbid. 



Subculture of this broth showed colonies of streptococci only. 



b. After 30 minutes : on agar no colonies; broth very slightly turbid. 

 Subculture of this broth showed colonies of streptococci only. 



c. After 1 hour : on agar no growth ; broth very slightly turbid 

 (streptococci). 



From this experiment it follows that the microbes of the coli- 

 typhoid type were completely disinfected in 15 minutes by izal 

 1 in 500 ; but the streptococci, although disinfected for agar in 

 30 minutes, were not quite disinfected for broth though very largely 

 reduced in number in 1 hour. 



Experiment 6. — The same stool (2) as in experiment 5 was treated 

 with izal 1 in 600, after exactly the same manner as described above. 



Result : — 



a. After 1 5 minutes : agar free of growth j broth slightly turbid 

 (B. coli). 



b. After 30 minutes : both tubes free of growth. 



c. After 1 hour : both tubes free of growth. 



Experiment 7. — The same stool (3) treated with izal 1 in 750. 

 Result : — 



a. After 15 minutes: agar showed 5 colonies (B. coli); broth 

 uniformly turbid (B. coli). 



b. After 30 minutes : agar shows 3 colonies (B. coli) ; broth 

 very slightly turbid (B. coli). 



c. After 1 hour : agar no growth ; broth no growth. 

 The result of these two experiments, 6 and 7, is then : — 



Izal 1 in 600 completely disinfected the microbes of the coli- typhoid 

 group in 30 minutes, but not in 15 minutes. Izal 1 in 750 completely 

 disinfected these microbes in 1 hour, but not in 30 minutes. 



Experiment 8. — Typical (pea-soup) typhoid stool (4) of a case, 

 19th day of illness, was treated in exactly the same manner as the 

 stool in experiment 5 — namely, 1 in 500 — with this result : — 



a. After 1 5 minutes : no growth on agar or in broth. 



b. After 30 minutes : no growth on agar or in broth. 



c. After 1 hour : no growth on agar or in broth. 



In this case, then, izal 1 in 500 caused in 15 minutes complete 



U 



