THE MICROSCOPE IN AETIOLOGY. 323 



has been greatly diminished since the systematic building 

 of sewers and the prohibition of pitlike privies in towns. 



Dr. Salisbury's observations on the growth of certain 

 fungi as the cause of malarious fevers, although requiring 

 further confirmation, suggest a very pertinent line of in- 

 quiry. 



Drinking-water may be vitiated by organic matter and 

 its chemical products, as ammonia, chlorine, and the ni- 

 trates. Wagner states that to be drinkable it must not 

 contain in 100,OuO parts more than 0.4 parts of nitric acid, 

 0.8 parts of chlorine, and 5 parts of organic matter. Boil- 

 ing does not improve such water. It is generally made 

 impure by sewage, and produces gastric and intestinal 

 diseases, arid perhaps typhoid fever. 



III. EXAMINATION OF FOOD, ETC. 



The adulteration of food has long been a question of 

 interest, and has been investigated by a host of observers. 

 Dr. Hassall's voluminous researches, however, leave little 

 to be desired. He states that "in nearly all articles, 

 whether food, drink, or drugs, my opinion is that adul- 

 teration prevails. And many of the substances emplo3 7 ed 

 in the adulterating process were not only injurious to 

 health, but even poisonous." Dr. Hassall's work, Food 

 and its Adulterations, should be used by all who inquire 

 into this subject, which is too voluminous to be considered 

 here in detail. Familiarity, however, with the subjects 

 already discussed in this work will qualify the observer 

 for such examinations. Wheat-flour may be examined 

 by adding a little water, and then a few drops of a solu- 

 tion of potash (one part liquor potassse to three of water). 

 Granules of potato-starch swell by this means to three or 

 four times their natural size, while those of wheat-starch 

 are scarcely affected by it. Comparisons of different kinds 

 of starch under the microscope will guide in many other 



