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THE NATIONAL CxEOGRAPHIC MAGAZINE 



the fish, and increase in size by accretions 

 of new matter around the margin ; these 

 accretions are in concentric zones hke the 

 rings of a tree. When the growth of an 

 eel ceases or is reduced, as in winter or 

 during a prolonged fast, there is a corre- 

 sponding discontinuity or decrease in the 

 deposition of new matter on the margin 

 of the scales, and such periods of ar- 

 rested growth are permanently marked 

 and enable the student to compute the 

 exact age of eels. 



Scales are not normally deposited until 

 eels have passed three years in fresh 

 water; they form first near the middle 

 of the side, and may not appear on the 

 head until two years later. Consequently, 

 in determining the age of any given speci- 

 men of eel by its scales, the side scales 

 should be those first deposited, and al- 

 lowance should be made for the scaleless 

 life (3 years) and the period spent at 

 sea after hatching (i year). 



DESTRUCTIVE HABITS OF THE EEL 



However much we may be interested 

 in the extraordinary habits of the eel, and 

 however much we may extol its food 

 value and economic importance, we can- 

 not ignore its injurious relations to other 

 fishes. 



The eel is not a fighter and beats a re- 

 treat when attacked by fishes of even 

 much smaller size than itself. It is not 

 destructive to fishes in the way that many 



of our best game and food fishes are, but 

 it preys extensively on small fry. 



The principal damage done by the eel, 

 however, is to the spawn of food fishes. 

 This is consumed in great quantities, es- 

 pecially at night. The shad and herring 

 are among the principal sufferers. The 

 eel, like the human species, has acquired 

 a taste for shad roe, and in the exercise 

 of this propensity it at times comes into 

 serious conflict with the fishermen of 

 some of the Atlantic rivers. 



Many years ago it was noted by Prof. 

 Spencer F. Baird, Commissioner of Fish- 

 eries, that the eel is an undesirable in- 

 habitant of streams in which fish are 

 caught by means of gill nets ; and that 

 there is a large destruction of shad and 

 herring in the Susquehanna and other 

 streams to the southward, where it is a 

 not infrequent experience of fishermen 

 to find, when their nets are hauled in, 

 that the greater part of the catch consists 

 simply of heads and backbones, the re- 

 mainder having been devoured by eels 

 in a short time, while spawning shad 

 caught in gill nets are sometimes found 

 completely emptied of roe. 



A curious experience, referred to by 

 Professor Baird and noted also by more 

 recent observers, is for a fisherman to 

 find a shad, apparently in full roe, to con- 

 tain an eel or several eels which have 

 entered the vent, destroyed the eggs, and 

 ensconced themselves in the abdominal 

 cavity of the shad. 



OUR ARMY VERSUS A BACILLUS 

 By Alton G. Grinnell 



IN ALL the history of human en- 

 deavor nothing compels greater ad- 

 miration than the devotion of a life- 

 time to the conquest of a world-wide dis- 

 ease. It is seldom, if ever, given to one 

 individual to search out single-handed 

 the cause of the disease, demonstrate to 

 humanity how it is communicated, and 

 show how it may be prevented. In such 

 a monumental achievement the ultimate 

 success is usually due to the researches 

 and experiments of many men, all of 

 whom have been actuated by an ambition 



to relieve human beings of unnecessary 

 suffering. 



The details of the first act of such a 

 drama are usually obscure, and even if 

 known to the public are uninteresting at 

 the time because of their technical char- 

 acter and apparent lack of connection 

 with human ills. 



But when the years of experimenta- 

 tion have passed and the marvelous thing 

 is demonstrated, with all the world the 

 stage, men wonder at the transformation. 



Typhoid fever, which before 1908 had 



