562 TROPICAL HYGIENE, SANITATION, ETC. 



The first was demonstrated in 1892 b_Y hvanowski, the mosaic 

 disease of the tobacco plant. 



In man we find the viruses of : — 



YeUow fever, which is destroyed at 53° C. in ten minutes. 



Dengue fever, Three days fever, Pappataci fever, Molkiscum con- 

 tagiosum, PohomyeHtis, Measles, Scarlatina, Verruca vulgaris, 

 Trachoma, Typhus, which is destroyed by a temperature of 55° C. 



Variola and Vaccinia are both destroyed at 58° C. in fifteen 

 minutes. 



In nearly every case the immunity produced by the disease is 

 complete. 



Secondary infections may give rise to many symptoms which may 

 be confused with the true symptoms of the original disease. 



It should be remembered that filtration of water will not aid much 

 in the prophylaxis of the above diseases. 



In advising as to water purification, all the facts of the particular 

 case must be taken into consideration. Thus if the water is derived 

 from a source free from human pollution and the ingredients to be 

 removed are suspended particles, colouring matter and iron in solution, 

 the mechanical filter will be sufficient. 



But if the water is or may be polluted, some process of storage, 

 sterilization, and slow sand filtration are necessary. 



Mechanical filters combined with storage will give a satisfactory 

 water supply in the majoritv of instances, but so'me waters will always 

 require an adequate sterilization process as in some parts of India 

 where pilgrimages are common. 



For important notes on the Bacteriology of Tropical Waters, see 

 p. 640, Section IX, Laboratory Hints. 



FOOD. 



NUTRITION. 



The essential constituents of food are : — 



(i) Nitrogenous, animal and vegetable albuminoids (proteins) and 

 gelatin. 



(2) Fatty, animal and vegetable fats and oils. 



(3) Carbohydrates, starches and sugars. 



(4) Salts, organic and inorganic. 



(5) \\^ater and vilamines. 



Nitrogenous foods are necessary for growth, maintenance, repair, 

 functional activity and in some measure the production of heat and 

 force for the body. 



Assimilation of excess of nitrogen, in the absence of exercise, leads 



