648 LABORATORY HINTS 



(4) Having regard to the variation in tiie bacteria in fceces, botli 



in quantitv and kind, no constant approximate composition 

 can be arrived at. Even in the large groups, suggested by 

 ]\IacConkey, variation in percentage composition in the same 

 animal is considerable. 



(5) Xo lactose-fermenting organism has been isolated by us that 



has been proved to be the inhabitant of the intestinal tract of 

 cattle or man only. 



(6) The numerical relation of the organisms constituting Mac- 



Conkey's groups in the intestines of cattle in India is entirely 

 dififerent from that in England, while in the intestines of man 

 it appears to be very similar in the two countries. 



(7) A study of the organisms present in faeces at different times of 



the year is necessary for the proper interpretation of the 

 results obtained from water analyses. 



The Bacteriology of Lake Water. 



(i) The action of the sun is powerful in destroying all faecal 

 organisms in water, particularly where they are " naked " 

 and not surrounded by mucus derived from the intestine. 



(2) All f^cal organisms do not possess the power of resisting the 



action of sunlight to an equal degree. 



(3) It is possible to divide f^cal organisms, with a reasonable 



degree of accuracy, into the following classes : — 



(a) The delicate organisms or those that are very susceptible to 



the action of sunlight. 



(b) An intermediate class containing a very large number of 



organisms which occupy an intermediate position between 

 the two extremes, and 



(c) The resistant organisms or those capable of resisting the 



sunlight for a considerable length of time. 



(4) The surface layers of any large volume of water are in conse- 



quence purer than the deeper ones. 



(5) Consequently the outlet from the reservoir should be arranged 



as near the surface as possible. 



(6) In the Red Hills lake, B. cloacae is by far the commonest faecal 



organism isolated from the bottom. 



(7) Coli communis even in large numbers, in a huge volume of 



water, disappears with great rapidil\'. The organisms never 

 survived longer than six days. 



(8) There is some evidence that the middle layers of water in the 



lake of over 12 ft. deep contain more water organisms and 

 more faecal bacilli than the bottom or the surface. When 

 taking samples the depth should be stated from which they 

 are taken. 



