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THE POPULAR SCIENCE MONTHLY. 



ent chicks. No significant effect followed the 

 feeding with slugs or sow-bugs, but the chicks 

 fed with earth-worms developed symptoms 

 of gapes. Experiments were made in artifi- 

 cial culture, and are described in the author's 

 paper. For prevention of gapes, Dr. Walk- 

 er recommends keeping the chickens away 

 from the ground by putting them on floors, 

 and destroying the earth-worm and its para- 

 site by some preparation fatal to both, such 

 as common salt ; asafcetida and garlic, which 

 have been relied upon to cure or prevent 

 gapes, had no effect upon the Sgngamus. 



Dr. Bickerton's Experiments in Colcr- 

 Blindness. T. H. Bickerton, of the Koyal 

 Ophthalmic Hospital, Moorfields, has re- 

 corded the results of his personal examina- 

 tions of 5,087 subjects, during five years, 

 for color-blindness. Holmgren's tests were 

 used. Of 3,087 men and boys tested, 179 

 failed at the first test (a very pale, pure 

 green), either by omitting green, or by put- 

 ting in some other color. Of these, 74 

 passed successfully the remaining tests, and 

 were considered to have but a very slight 

 chromatic defect, which might be disregard- 

 ed. Rejecting these, there were 105 cases 

 of color-blindness, or 3 - 40 per cent of the 

 whole number. Of 1,841 women and girls 

 examined, 3 only, or - 162 per cent, were to 

 a greater or less extent affected, and of 

 these one so slightly affected that it was 

 cast out, leaving 2 pronounced cases, or 

 0"108 per cent. Sixty-four male lunatics 

 afforded 1 complete and 1 incomplete case, 

 while 95 female lunatics were all correct. 

 The social status of these and other persons 

 examined varied from the lowest to the 

 highest, and the ages ranged from five 

 years upward. A large majority of them 

 were under twenty-one. Besides those in- 

 cluded under the head of very slightly col- 

 or-blind, there were others whose color-per- 

 ception was feeble. Among the lower social 

 grades, as represented by the children in 

 orphanages and reformatories, a consider- 

 able number made mistakes in the exami- 

 nations, and these errors were made not 

 only by those of dullish intellects, but also 

 by those who, according to their mistresses, 

 were sharp girls. Cases of this kind were 

 retested after some months' tuition in colors, 

 and in most instances, where ignorance was 



suspected, the second trial proved the cor- 

 rectness of that conclusion ; but there were 

 others who, although they fulfilled the test, 

 did it with the utmost difficulty. Of the 

 105 cases of color-blindness, Dr. Bickerton 

 further remarks : " Not one so affected was 

 aware of the defect, and a number of them 

 do not believe it to this day. It may seem 

 curious that people who can not distinguish 

 as different colors red, green, and brown, 

 and in some few cases blue and yellow also, 

 do not themselves discover their peculiarity 

 in their vision for colors. Yet, strange as 

 it may be, so it is, and you will find it ex- 

 ceptional for a color-blind to realize in tho 

 first instance the defect himself." 



Effect of Climatic Changes on Species. 



Any theory of the distribution of species, to 

 be acceptable, must take account of the great 

 gaps which appear in the extension of many 

 kinds. Mr. Edward Forbes and many other 

 modern botanists believe that the question 

 is one of changes of climate ; or that the 

 climatic variations of the past are reflected 

 in the fauna and flora of the present. Their 

 views are partially confirmed by the obser- 

 vations which Professor A. Blytt, of the 

 University of Christiania, has made of the 

 climatological relations and the distribution 

 of plants in Norway. Nearly all the clima- 

 tological lines there run more or less in the 

 shape of the coast, so that the climates are 

 ranged in bands, the changes being observed 

 as one goes from the interior toward the 

 sea, or vice versa. In keeping with the 

 same are the variations of the flora. The 

 plants may be divided into groups, wherein 

 the species belonging to the same group 

 have a somewhat similar extension, while 

 each of the groups is confined to special 

 climatological conditions, and is found only 

 in those parts where the conditions corre- 

 sponding with its nature prevail. The flora 

 is generally monotonous ; but there are cer- 

 tain places dependent partly, perhaps, on 

 the character of the soil, but as much upon 

 exposure to the sun and protection from 

 the changeableness of the coast climate, 

 where a rich vegetation may be found. 

 The flora is destitute of peculiarly charac- 

 teristic species, because it has come to the 

 country by immigration after the Glacial 

 period, from other countries which were 



