642 . LABORATORY HINTS 



(6) The bacterial flora of human origin is very different to that of 



animal origin and reasoning based upon the formisr and 

 applied to the latter in tropical climates may often lead one 

 into very serious error. 



(7) The worker will find that high winds laden with dust will gain 



access to his plates and colonies and repeatedly ruin his works. 

 Each district water supply must be judged on its merits. 

 Data from many different parts of the tropics must be provided 

 before standards of impurity can be generally recommended and 

 adopted. 



The first data came from : — 

 Daniels in Malay. 



Balfour and Archibald in the Soudan. 

 Clemesha in India. 



(A) Daniels working in the Federated Malay States (1908) proposes 

 the following as a basis : — 



(i) The number of organisms (exclusive of known, easily recog- 

 nized, non-pathogenic organisms, e.g., B. subtilis, B. 

 megaterium, B. violaceus, and some of the organisms which 

 form characteristic yellow colonies) which have been proved 

 to be non-pathogenic to lower animals, 



(2) The amount of the water required to react, forming acid and 



gas, with MacConkey's medium, from o'2 to 2 c.c. being 

 employed in the tests. 



(3) Indol formation in forty-eight hours in peptone water with 



10 c.c, 5 c.c. and i c.c. of the water to be tested. 

 As a standard Daniels and Finlayson suggest that : — 

 (i) Not more than 100 organisms, exclusive of those mentioned, 



should be present in i c.c. of the water. 



(2) That no acid and gas should be formed in twenty-four hours 



in MacConkey's medium at 37° C. with 2 c.c. of the water. 



(3) That no indol should be formed in peptone water in forty-eight 



hours with 5 c.c. of the water added. 



They remark that the standard is not a high one but it is exceptional 

 to find a natural water that will pass all three tests. 



In unprotected shallow wells liable to be polluted bv surface wash- 

 ings, they found the average bacterial count to vary between 300 to 

 900 per c.c, while in twenty-three out of twentv-seven wells examined, 

 acid and gas forming organisms were present in 3 c.c. and usually in 

 4 c.c. of the water, and indol formers in 5 c.c. in the case of ten of the 

 wells. B. pyocaneus was found in one instance, and in two cases 

 organisms indistinguishable from B. coli communis. 



(B) Balfour and Archibald have done good work in the Soudan 

 in connection with river and shallow well water in Khartoum. 



