78 



SCIENCE. 



[Vol. X. No. 236 



statement could be accepted without much qualification, we might 

 derive great comfort from the assurance that chemical examination 

 of soils shows the presence, within reach of the plough, of nine 

 thousand pounds of potash, and half as much phosphoric acid, on 

 every acre, or enough to furnish the average crop for from two hun- 

 dred and twenty-five to two hundred and fifty years. 



Now, in the first place, the average land in tillage at the present 

 time by no means reaches such a standard ; and, in the second 

 place, it is well known that but a very small fraction of the plant- 

 food actually present in soil is in an available form. Ordinarily 

 more than ninety-nine per cent of the plant-food found in soil by 

 the chemist the plant itself finds dormant or unavailable. Time 

 and natural agencies gradually convert their inert elements ; but, 

 to keep pace with agricultural demands, the physical properties of 

 soils must be closely studied, and knowledge obtained and applied 

 regarding the proper mechanical treatment of land. Figures already 

 sufficiently demonstrate the recognized condition and needs of the 

 soil. So difficult is it to make the once fertile land take back into 

 use the natural resources, and so active the demand for plant-food 

 in every available form to return to the soil, that, incredible as it 

 appears, commercial fertilizers are maintained at such selling rates 

 as to make the entire annual farm-products of this country worth 

 half as much for manure as they are in market. 



With our rapidly increasing population, and a constantly lessen- 

 ing fertility of soil, we have presented to us questions of the gravest 

 import. By the wasteful processes prevailing, we are expending 

 our very substance, and daily adding to a burden under which 

 generations to come will stagger. 



The true economy of soil management, involving the production 

 for our people of food and clothing, fuel and shelter, and the wise 

 management and disposition of our surplus, are problems great 

 enough to satisfy the ambition of both scientists and statesmen. 



In all expositions of the condition and prospects of the agriculture 

 of this country. Gen. Francis A. Walker claims that the American 

 people have been fully justified, upon sound economical principles, 

 in the past system of cultivation of the soil at the expense of future 

 generations. 



" Thirty-eight noble States, in an indissoluble union, are the justi- 

 fication of this policy. Their school-houses and factories, their 

 roads and bridges, their railways and warehouses, are the fruits of 

 the characteristic agriculture of the past." 



But the reason for wasteful systems no longer exists. " The 

 country in the arable parts is settled, and the line of population 

 now rests near the base of the great sterile mountains which oc- 

 cupy so large a portion of the continent. ... A continuance of 

 this policy will be, not the improvement of our patrimony, but the 

 impoverishment of our posterity. . . . Economical and political 

 considerations alike demand that the soil bequeathed to this gen- 

 eration, or opened up by its own exertions, shall hereafter be deemed 

 and held as a sacred trust for the American people through all 

 time to come, not to be diminished or impaired for the selfish en- 

 joyment of its immediate possessors." 



These considerations should increase our regard for and interest 

 in the business of farming. We should all rejoice at the revival of 

 agricultural studies, and the increasing number of able men who 

 are making them their life's work. 



Let me cordially invite continued contributions to the proceedings 

 of this section, upon foods, fabrics, forestry, industrial education, 

 and other topics closely related to our material welfare. And I 

 appeal for more encouragement and aid for the earnest workers in 

 other sections, — in biology and chemistry, physics and mechanics, — 

 who are laboring in the various branches of science, that its practi- 

 cal results may be applied to economizing the fertility of the soil, 

 which is the basis of our material prosperity. 



MENTAL SCIENCE. 



The Sense of Smell in Dogs. 



Dr. G. J. Romanes, by his careful observations and happy 

 generalizations, has made himself the representative of the growing 

 science of comparative psychology. His two books on animal in- 

 telligence and on mental evolution in animals (to which is to be 

 added a third on the mental evolution of man), written under the 



inspiration of Dar^vin, have done more, perhaps, than the works of 

 any other writer, to introduce scientific order into a field formerly 

 given over to poorly described, exaggerated stories, and hasty, un- 

 warranted generalizations. With the downfall of the anthropo- 

 morphic theory of the universe, the importance of the mental phe- 

 nomena observable in animals was more readily recognized and 

 appreciated. Hundreds of observations drawn up with the requisite 

 details and accuracy have been collected, and a number of reliable 

 and suggestive generalizations have been recorded. To these Dr. 

 Romanes has added an important study on the method by which 

 his dog follows the scent of the master. 



The observations were made on Dr. Romanes' setter-bitch, an 

 animal very much attached to him. They were made on the 

 grounds adjoining his house, and a number of precautions not 

 easily described were taken, (i) When Dr. Romanes walks over 

 the ground with his hunting-boots on, the dog follows the scent 

 with the greatest readiness. (2) If she is put to the track of a 

 stranger, she pays no attention to it. (3) The dog was led into the 

 room when preparations were going on for an outing, but, instead 

 of Dr. Romanes going out, the gamekeeper (whose scent he follows 

 next after that of Dr. Romanes) went : when set free, the animal at 

 first followed the track, but, finding that her master was not with 

 the gamekeeper, returned. (4) The next experiment was a very in- 

 genious one. Twelve men walked in Indian file, so that they all 

 trod the same footsteps, thus producing a conglomerate of olfactory 

 impressions. Dr. Romanes headed the company, so that the traces 

 of his steps should be most obliterated ; and, after walking thus 

 two hundred yards, the first six men walked in one direction, the 

 last six in another. The dog quickly ran along the route followed 

 by the twelve, overshot the point of division, but soon returned and 

 followed the direction taken by the six headed by Dr. Romanes. (5) 

 A number of experiments were made to ascertain what part of Dr. 

 Romanes' person or of his apparel gave the clew to the animal. It 

 was suspected to be the hunting-boots, and this proved correct. A 

 stranger put on these boots, and the dog eagerly followed the 

 scent ; and, contrariwise, when (6) Dr. Romanes put on the stranger's 

 boots, the animal was indifferent to his track. (7) Further e.x- 

 periments were made to locate the source of the scent in the boots. 

 The dog did not follow the scent of a stranger walking in bare feet. 



(8) When Dr. Romanes walked in bare feet, the dog followed the 

 trace, but less eagerly than usual, and with much hesitation. 



(9) Again, the animal did not follow Dr. Romanes when he 

 put on new shooting-boots. (10) Next a single sheet of brown 

 paper was glued to the soles of his usual hunting-boots. The dog 

 did not catch the trail until he came to a place where, as Dr. Ro- 

 manes had previously noted, a few square millimetres of the paper 

 had come off. (11) When her master walked in new cotton socks, 

 the trail was lazily followed, and soon given up. With woollen 

 socks worn all day the result was the same. (12) Dr. Romanes 

 next walked fifty yards in shooting-boots ; then three hundred yards 

 in his stocking-soles, carrying his boots ; then three hundred yards 

 in his bare feet. The animal caught the scent, and followed it 

 unhesitatingly through the whole distance, though the trace left by 

 stockings or bare feet alone was not sufficient to guide the animal. 

 (13) The next test was a modification of the last. Dr. Romanes 

 and a stranger entered a carriage and drove for several hundred 

 yards. The former, in his hunting-boots, then alighted and walked 

 fifty yards, whereupon he re-entered the carriage, and the stranger 

 walked the next two hundred yards : the dog, when shown the 

 track, ran the whole two hundred and fifty yards without pausing. 

 The experiment was repeated with another stranger, with the same 

 result. (14) To test the power which the dog had of selecting the 

 distinctive odor accompanying her master from other odors. Dr. 

 Romanes soaked his hunting-boots in anise-seed-oil. The odor was 

 so strong that a friend could follow the track an hour later by the 

 odor of the oil ; yet the dog was not confused except that she hesi- 

 tated about the first few steps, but then pursued as usual. 



The next test was directed towards ascertaining whether the ani- 

 mal could distinguish her master by odors emanating from other 

 portions of his person, (i 5) Dr. Romanes, after pursuing a zig- 

 zag course just trodden over by a number of footsteps, hid behind 

 a wall, with his eyes just visible. The animal went at once to the 

 hiding-place. (16) Again he hid in a ditch, with only the top of 



