696 



PHYSIOLOGY. 



with the amounts found at the end of the ex- 

 periment in the residual solution and plants. 

 The excess of the latter amount over the for- 

 mer, which was in some cases very large, must 

 represent nitrogen acquired in some way from 

 the atmosphere. In a second series of experi- 

 ments, the conditions of growth were varied 

 by varying the concentration of the nutritive 

 solutions ; by varying the total quantity of 

 food supplied to the roots by the solutions, 

 from an amount seemingly sufficient, or nearly 

 so, for normal growth, to a very scanty supply; 

 and by varying the proportion of nitrogen in 

 the solution. The results of the experiments 

 showed that the plants grown in nutritive so- 

 lutions (containing potassium and calcium ni- 

 trates, potassium phosphate, magnesium sul- 

 phate, and ferric chloride), exposed to the air, 

 but protected from rain and dew, contained at 

 maturity more nitrogen than was supplied them 

 in nutritive solution and seed. For this excess 

 of nitrogen there was but one possible source, 

 namely, the atmosphere. Under variations of 

 the conditions of growth, the gain of nitrogen 

 was always largest when the conditions of 

 growth were most nearly normal, and smaller 

 as either condition was made abnormal. The 

 amount of nitrogen acquired from the atmos- 

 phere rose and fell with the amount of food at 

 the disposal of the roots, being largest where 

 the plants were tolerably well fed, and small- 

 est where the food-supply was inadequate. So, 

 likewise, where the supply of nitrogen varied, 

 the amount of mineral food remaining the same, 

 the plants acquired more or less aerial nitro- 

 gen in proportion as more or less nitrogen was 

 supplied to them in the nutritive solution. In 

 the trials which were made with solutions suf- 

 ficiently dilute to permit normal assimilation, 

 the very poorly-fed plants obtained one third, 

 and the tolerably well-fed ones one half of 

 their whole nitrogen from the air. How and 

 in what form this nitrogen was acquired, says 

 Prof. Atwater, the experimentsdo not tell. "It 

 must have come to the plants as either com- 

 bined nitrogen ammonia, nitric or nitrous acid 

 or as free nitrogen. It must have been either 

 taken directly by the foliage, or first absorbed 

 by the nutritive solution and communicated by 

 it to roots. That the whole, or indeed any con- 

 siderable portion, could have been gathered 

 from the air and conveyed to the plants by the 

 nutritive solution, which was neutral or slight- 

 ly alkaline during growth, is, to say the least, 

 in direct apparent contradiction with the best 

 experimental evidence at hand. The hypothe- 

 sis of the absorption of any considerable quan- 

 tity of combined nitrogen by the leaves of the 

 plants is directly opposed as well to the testi- 

 mony of the most reliable experiments upon 

 the subject as to the seemingly unanimous opin- 

 ion of the men who have made them. The 

 only remaining hypothesis is that of the assimi- 

 lation of the free nitrogen of the air by the 

 plants. This is likewise contrary to the results 

 of the best investigations. A way out of the 



difficulty may, perhaps, be found in the obser- 

 vation by Berthelot of the assimilation of free 

 nitrogen by vegetable matter through the aid 

 of electricity of a potential similar to that 

 which obtains in the air near the surface of 

 the earth ; an agency which may have been 

 excluded in the experiments which are most 

 decisive against the assimilation of free nitro- 

 gen." 



Bibliography. The most important physio- 

 logical publication of the year is Dr. Stirling's 

 translation of the treatise of Landois. R. Blan- 

 chard has published the first part of a work on 

 " Medical Zoology." Vogt has written a "Com- 

 parative Anatomy," and Colin has prepared a 

 new and improved edition of his " Compara- 

 tive Physiology." Continued additions have 

 been made to the general stock of knowledge 

 in the successive publications of the results of 

 the Challenger Expedition, under the direction 

 of Dr. Murray, which are to appear in a series 

 running up to fifteen or more volumes. Ret- 

 zius has completed his great work on the "Anat- 

 omy of the Ear." F. Leydig has written an 

 elaborate account, enriched with original ob- 

 servations, of " Cells and Tissues." Among 

 the shorter memoirs and papers of a more spe- 

 cial character are those of Zacharias on tte 

 nucleoli of cells; of Henhum, of Stockholm, 

 on the forms of cells and the appearance they 

 present in section ; Fleischl's device of a hse- 

 mometer, or instrument for determining, by the 

 colorimetric method, the globular richness of 

 .the blood; the experiments of Otto on the 

 number and richness in haemoglobin of the cor- 

 puscles of the blood in men and women re- 

 spectively ; and of Munk on the mode of ab- 

 sorption and the origin and mode of deposition 

 of fat in the body. Bearing upon the nervous 

 system are Christiani's studies in the " Physi- 

 ology of the Brain," especially in reference to 

 the relations of the hemispheres to the power 

 of sight, and to the existence of two centers of 

 respiration, one inspiratory and pupil-dilating, 

 and the other expiratory and pupil-contract- 

 ing ; the observations and experiments of Ott, 

 Richet, Aronsohn, and Sachs, on the presence 

 of a heat-center of the brain ; Exner's obser- 

 vations on the localization of the visual center, 

 which support those of Christiani, and are in 

 opposition to those of Munk, Dalton, Ferrier, 

 Luciani, and others ; the studies of Kirchhoff 

 in localizing the ano-vesical center in man ; of 

 Bechterew, Edinger, and Flechsig, on the con- 

 stitution and development of the posterior col- 

 umns of the cord ; and of Sandemann on the 

 ultimate distribution of motor nerves. Ewald 

 and Boas have investigated the presence of 

 lactic acid along with the products of digestion. 

 Prof. Maggiorani has made experiments on the 

 influence of powerful magnetic currents on the 

 development of the egg of the fowl. The rapid 

 progress of histological research has suggestei 

 a more frequent publication of the " Quarterly 

 Journal of Microscopic Science." Among the 

 articles that appeared in this branch during the 



