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THE POPULAR SCIENCE MONTHLY.

same ancestor was once surprised by hearing some one speak of his father's sleigh as being green on the outside and red on the inside, for it had always appeared to him to be of the same color on both sides. He was also heard to remark that he could see no change in the color of the maple-leaves, which, as we all know, turn from their summer green to red, and then to brown. This form of color-blindness is particularly inconvenient to persons who wish to pick cherries or strawberries, for they have only the forms to guide them, without any help from the color. One of the brothers of the grandfather and two of his first-cousins had the same defect, and a nephew in the next generation. The youth spoken of in the beginning of this notice is the first in the present generation who has manifested it. Generally the affection appears to have been transmitted through the female line of the family, but to sons, and not to daughters. Exceptions to this rule are noticed in the case of a great-uncle of the youth's mother, who inherited it from his father and transmitted it to his four sons; and of a female relative, through whom it was transmitted to two daughters. By means of the instances related, the course of the affection is traced through five generations.

 

Why Prairies are Treeless.—Mr. Thomas Meehan believes that we have nearly reached the solution of the question of the cause of the absence of trees from the prairies. It is not climatic, for timber-belts flourish in all the prairie regions. It is not in conditions of soil, for the prairie soil is the most favorable to the germination of seeds, of trees as well as of other plants, and artificial plantations are remarkably successful wherever they are made. The real cause is probably to be found in the annual fires which have swept over the prairies from time immemorial, killing the young trees before they can grow large enough to resist the heat. The seeds of the annual plants of the prairie vegetation, maturing every year, are shed and find protection before the fires come; the young trees, on the, other hand, bear no seed, and can leave no resource for a succession after they are burned. This theory is supported by the fact that an abundant growth of trees has set in wherever the fires have been stopped. The fires were made by the aborigines for centuries before the white men came, possibly for the express purpose, Mr. Meehan suggests, of preventing the growth of trees and preserving the buffalo-pastures. The question remains how the prairies first came to be naked. They probably formed the bottoms of the lakes and marshes that were left after the retreat of the glaciers, and continued wet after the highlands were covered with trees. Man followed the glaciers so closely that he anticipated the trees on these spots, and, having learned already in southern latitudes the value of burnings, began them before the trees gained a foothold.

 

Darwin's Views on Vivisection.—The following is Mr. Darwin's reply to a letter from Professor Holmgren, of Upsala, requesting his views on the right to make experiments on living animals in the interest of science:

Down, Beckenham, April 14, 1881.

Dear Sir: In answer to your courteous letter of April 7th, I have no objection to express my opinion with respect to the right of experimenting on living animals. I use this latter expression as more correct and comprehensive than that of vivisection. You are at liberty to make any use of this letter which you may think fit, but if published I should wish the whole to appear. I have all my life been a strong advocate for humanity to animals, and have done what I could in my writings to enforce this duty. Several years ago, when the agitation against physiologists commenced in England, it was asserted that inhumanity was here practiced, and useless suffering caused to animals; and I was led to think that it might be advisable to have an act of Parliament on the subject. I then took an active part in trying to get a bill passed, such as would have removed all just cause of complaint, and at the same time have left physiologists free to pursue their researches—a bill very different from the act which has since been passed. It is right to add that the investigation of the matter by a Royal Commission proved that the accusations made against our English physiologists were false. From all that I have heard, however, I fear that in some parts of Europe little regard is paid to the sufferings of animals, and if Ibis be the case I should be glad to hear of legislation against inhumanity in any such country. On the other hand, I know that physiology can not possibly progress except by means of experiments on living animals, and I feel the deepest conviction that he who retards the progress of physiology commits a crime against mankind. Any one