82 THE AMERICAN MONTHLY [May 



living- plants, including" bacteria, animals, and inorganic 

 matter in such a way that the result can readily be 

 weighed, the volume determined, the number of particles 

 counted under a microscope, and tables constructed to 

 show the yield of an}^ g-iven area of water. This method 

 is applicable in the artificial propagation of food fishes 

 since it collects the microscopic plants and animals which 

 constitute the food of newly hatched fry. The suitability 

 of water for receiving any fish is as much dependent upon 

 the microscopic food it contains as on its temperature. 



Malted Milk Lunch Tablets. — These lozeng-ers are 

 conveniently carried in the pocket and available on trips 

 when one is hungry, faint or exhausted. They contain 

 concentrated food representing- the nutritive elements of 

 milk and the cereals. Being free from starch and cane 

 sugar they do not appeal to a disorded appetite. Other- 

 wise they would replace all kinds of candy and ought to do 

 so in spite of that fact. The Horlick Food Co., Rachine, 

 Wis., send out sample packages to doctors, teachers and 

 editors free of charge. 



SCIENCE-GOSSIP. 



Sewage Purification. — At Barking, England, there are 

 biological filter-beds. The measurement of purification at- 

 tained is taken (a) from the amount of oxygen absorbed; 



(b) from the amount of albuminoid ammonia got rid of; and 



(c) the increase in the quantity of nitrates. By passing 

 the sewage intermittently through these filters and by al- 

 lowing them to rest and become aerated between the 

 charges, it was found that a purification of from 41 to 85 

 per cent was obtained, the whole of the organic matter was 

 completely removed and an effluent fit to be discharged 

 into rivers was obtained. The purification g-oes on at the 

 rate of 750,000 gallons per acre of biolog-ical filter. At 

 Sutton, England, a little different process is used, the fil- 

 trate from one bacteria tank being passed through a sec- 



