n.2 



KNOWLEDGE. 



October, 1910. 



that the flesh of different kinds of animals could thus be 

 differentiated. 



For instance, a 20 per cent, aqueous extract of the flesh of 

 a horse was injected into rabbits, which were then killed after 

 a month. The clear filtered serum from the treated rabbit now 

 gave a precipitate with an extract of horse's flesh, but not 

 with that of any other animal. In like manner the serum of 

 a rabbit which had been rendered specific by treatment with 

 an extract of rabbit's flesh, gave a reaction with the extract 

 of the flesh of any other rabbit, but not with that prepared 

 from the flesh of a hare, a cat, or any other animal. 



The further application of the method to the examination of 

 blood soon suggested itself, and the process was studied by 

 Dr. de Nobele (.4);;;. Cliini. Anal., 1902, 7. 150), who proved 

 that the serum from a rabbit or mouse into which human 

 serum had been injected gave a precipitate with the serum of 

 human blood, but not with that from the blood of animals. 



Even blood stains several months old, when dissolved in a 

 dilute solution of sodium chloride, gave the reaction, though a 

 stain nine years old failed to react. All attempts to prepare 

 a specific serum by feeding the animal with a particular scrum 

 instead of by inoculation proved unsuccessful. 



It was found that the serum could be evaporated in a 

 vacuum without destroying its activity, and that the dry residue 

 could be kept unaltered for manx- months and simply re-dissolved 

 when required for use. 



Later investigations showed that the test was not so 

 absolutely specific as was first believed, since when a very 

 concentrated solution of blood serum was used, a precipitate 

 was obtained in any case, though it was much smaller in 

 amount than when the blood serum and specific serum 

 corresponded, ^\■ith a diUition of one part of blood serum in 

 one thousand, however, the tests were always reliable. 



The first occasion upon which this test was employed in 

 criminal work was in a trial that took place in France some 

 five years ago. The prisoner had stated that a blood stain 

 had been caused by the blood of a rabbit. A serum specific 

 for rabbit's blood-serum was therefore prepared, and when 

 this gave no precipitate within thirty minutes with an extract 

 from the stain it could be stated with certainty that no rabbit's 

 blood was present. 



ACTION OF LEAD ARSENATE ON FOLIAGE.— 

 A recent Bulletin of the U.S. Dept. of Agriculture (No. 131), 

 contains an account by Messrs. Haywood and McDonnell of 

 the effect of lead arsenate upon plants. Preparations of this 

 compound are now extensively used to protect fruit trees 

 against the larvae of the gypsy moth, and, provided no arsenic 

 passes into solution, do not appear to be injurious. Thus in 

 one year the fohage of apple and peach trees was not affected 

 by the treatment, whereas the same substance caused great 

 damage in another year when the atmospheric conditions were 

 more favourable for the decomposition of the lead arsenate. 

 The presence of small quantities of salts in the water used for 

 the dilution had also an influence on the decomposition. 



The composition of the commercial preparations varies 

 widely, as does also the product made by any of the published 

 recipes. In anv case the arsenic ought not to be present 

 except in complete combination with the lead. An addition 

 of lime to the liquid was found to reduce the tendency to 

 injure the foliage. 



ABSORPTION OF loUINE BV SOLID SUBSTANCES. 

 — A considerable amount of iodine may be absorbed by solid 

 substances when exposed to air saturated with iodine vapour, 

 the degree of absorption depending on various conditions, such 

 as the nature and physical condition of the material. The 

 details of an investigation of the phenomenon are published by 

 M. Guichard in the Coiiiptes Rcndiis (1910, Vol. 151,236), 

 and the following particulars are typical of the results 

 obtained : — Silica, whatever its physical condition, only absorbs 

 an insignificant amount of iodine (not e.xceeding O'S per centl. 

 On the other hand, alumina calcined at various temperatures 

 up to 600° C. takes up amounts varying from I'S to 16 per 

 cent., but after being fused absorbs none at all. In like 

 manner calcined magnesia absorbs from 0'4 to IS'9 per cent.. 



the variations depending upon the temperature at which it 

 was calcined and the salt from which it was prepared. The 

 effect of raising the temperature of the calcination is probably 

 to reduce the spaces between the particles, and the cessation 

 of absorption after fusion is probably an indication of the 

 disappearance of these intergranular spaces when the maximum 

 density is reached. The colours of the substances after the 

 absorption vary with the amount of iodine absorbed. 



FXONOMIC BIOLOGY. 



By Walter E. Collinge, M.Sc, F.L.S.. F.E.S. * 



THE REST PERIOD IN PLANTS.— The winter rest 

 period of plants is a subject of considerable economic im- 

 portance, and the results of numerous experiments have shown 

 that bv different modes of tre.atment they may be aroused 

 from this resting state or may be caused to omit their ordinary 

 habit of resting and grow continuously. 



The latest contribution to the subject is a most interesting 

 memoir by Professor \\'. L. Howard, of the University of 

 Missouri .Agricultural Experiment Station {Research Bull., 

 No. 1, 1910). in which he sets forth the results of a most 

 elaborate investigation upon this subject. 



As a result of extensive studies and experimentation he 

 concludes that nearly all fruit trees and ornamental shrubs 

 have definite resting periods, i.e.. each species, and possibly 

 each variety, has a certain number of days during which it 

 will not grow under natural conditions. But the great 

 majority of species do not have this winter period of rest so 

 firmly fixed that they cannot be awakened from it. Un- 

 favourable external conditions determine both the time of 

 occurrence and the degree of intensity of the period, and if 

 these unfavourable conditions occur at regular intervals, a 

 plant readily adapts itself to the new demands, and the rest 

 iDeconies a habit which may continue to be repeated auto- 

 matically for a longer or shorter period of time. 



Tlie Practical Application. — .4 practical application of 

 the above principles is cited in connection with the peach. 

 This tree is known to have a comparatively short resting 

 period (about six weeks), and is frequently liable to injury in 

 late winter by frost owing to the habit of premature growth 

 during warm days in late winter. If the trees could be caused 

 to continue growing later in the autumn, they would con- 

 tinue dormant a correspondingly longer period in late winter. 



Professor Howard concludes " If it were known definitely 

 that plants have a tendency to grow at unseasonable times by 

 reason of the fact that they have very slight resting periods, 

 or that the resting stage is at an end. we might then set about 

 devising means for regulating the period of dormancy, or, 

 knowing that their habits of growth in this respect cannot be 

 easily changed, of finding means for protecting them." 



GR.AIN WEEVILS. — A correspondent writes requesting 

 some information as to the conditions that favour the breeding 

 and development of grain weevils. Some years ago Mr. F. J. 

 Cole published the results of a series of most interesting 

 experiments ijoiirn. Ec. Biol., 1906), and more recently I 

 have supplemented these ijoiirn. Inst. BrCK-ing. 1907). The 

 conclusions arrived at as a result of these experiments were, 

 briefly, as follows : — " That moisture, with the appropriate 

 temperature (SO" F.) is very favourable to the adult insect ; 

 but the same temperature without moisture is fatal. A non- 

 ventilated atmosphere at about 80° F., charged with water 

 vapour (no matter how poor in oxygen, and contaminated with 

 carbolic acid gas), provides the most favourable conditions 

 for the life and reproduction of these insects. They can 

 flourish in a non-ventilated atmosphere, even when containing 

 as much as SO per cent, of CO>, if moist. Further, it was 

 shown that they can live in an atmosphere rare in oxygen 

 provided moisture is present. 



The conditions under which grain-eating insects live is only 

 very imperfectly known, and careful experiments with such genera 

 as Triholitim. Gnathoccrus. Tenebrio. and so on, would on 

 doubt bring to light many points of great biological interest, 



