May 13, 1909J 



NA TURE 



6^1 



mannc-r in which electrolytes produce this fall is by causing 

 aggregation of molecules to form particles. This is the 

 case whether acid, alkali, or neutral salt be in question. 

 The action of a stable colloid in protecting against the 

 effect of electrolytes is shown to consist, in the cases of 

 congo-red and of arsenious sulphide, in the production of 

 minute aggregates, which, although causing fall in 

 osmotic pressure by diminution of effective concentration, 

 are not of sufficient size to precipitate. Hence the pro- 

 tective power can only be regarded as a limited one, due 

 probably to the formation of complex colloids. The free 

 acid of congo-red forms a deep blue colloidal solution 

 when dialysed. This is easily resolvable under the ultra- 

 microscope, but gives a definite and measurable, though 

 small, osmotic pressure, about 14 mm. Hg for a i per 

 cent, solution. Assuming the kinetic theory to be correct, 

 this means that the aggregates contain, on an average, 

 twenty molecules. Estimations of the molecular dimensions 

 of this blue colloid were made on the basis of enumeration 

 of the particles in unit volume by means of the ultra- 

 microscope. The values found are larger than the accepted 

 ones for water, &c., about 100 times, in fact. The whole 

 of the results are capable of explanation on the assump- 

 tion that colloidal particles possess the kinetic energy of 

 molecules, but lend no support to any view that postulates 

 the necessary presence of foreign electrolytes. — The origin 

 and destiny of cholesterol in the animal organism. Part 

 V. — On the inhibitory action of the sera of rabbits fed on 

 diets containing varying amounts of cholesterol on the 

 haemolysis of blood by saponin : Mary T. Fraser and 

 J. A. Gardner. In an earlier paper it was shown by 

 comparative estimations of the total cholesterol-content of 

 the blood of rabbits that had been respectively fed on 

 ether-extracted bran, and on the same extracted bran with 

 the addition of known amounts of cholesterol, that some, 

 at any rate, of the cholesterol absorbed found its way 

 into the blood-stream. It seemed desirable to ascertain 

 whether the cholesterol was absorbed into the blood-stream 

 as such, or in the form of esters, or in both states, and 

 also whether the phytosterol of vegetable food can be 

 utilised for the formation of cholesterol in the organism. 

 Use was made of the observations of Hausmann, ."Xbder- 

 halden. and Le Count, who showed that, whereas 

 cholesterol and phytosterol inhibit the hemolytic action of 

 saponin, their esters do not do so. A series of compari- 

 sons were made of the inhibitory action of sera of rabbits 

 fed on extracted bran alone, on extracted bran, and, in 

 addition, measured quantities of cholesterol, cholesterol 

 esters, and phytosterol, respectively, on the haamolytic 

 action of saponin. Care was taken to keep the animals 

 under strictly comparable conditions, and the different sets 

 of hremolytic experiments were carried out under diverse 

 conditions. Conclusinns. — (i) When cholesterol is given 

 with the food of rabbits, some is absorbed, and finds its 

 way into the blood-stream as free cholesterol ; only a 

 portion of the total cholesterol given in the food is 

 absorbed, the rest being excreted unchanged. (2) Choles- 

 terol when in the form of esters undergoes hydrolysis in 

 part, at any rate, during digestion, and appears in the 

 blood-stream as free cholesterol. (3) When animals are 

 fed on phytosterol, this substance is in part absorbed, 

 just as in the case of cholesterol, and appears in the 

 blood-stream either itself or in the form of cholesterol. — 

 Some effects of nitrogen-fixing bacteria on the growth of 

 non-leguminous plants : Prof. W. B. Bottomley. 

 Bacterial cultures prepared from the algal zone of Cvcas 

 tubercles taken from below the surface of the soil alwavs 

 contain a species of Azotobacter associated with Pseudo- 

 monas radicicola. Pure cultures of these organisms were 

 obtained, and it was found that when they are growing, 

 in association there is an increased assimilation of free 

 nitrogen. 



Control 0-48 mgr. N. per 100 c.c. 



Pseudomonas alone ... o'gi ,, ,, 



Pseudomonas + Azotobacter I'2I ,, ,, 



In Cycas tubercles the bacteria live, usually imbedded in 

 a slime, in the open spaces of the algal zone, and the pro- 

 jecting cortical cells presumably absorb the nitrogenous 

 produiis of bacterial activity. Experiments made to ascer- 

 tain to what extent, if any, a mixed culture of Pseudo- 



XO. 2063, VOL. 80] 



monas and Azotobacter applied to the roots of other non- 

 leguminous plants might influence their growth, the 

 nitrogenous bacterial products being absorbed directly by 

 the plant, gave the following results : — Oats. — Pot experi- 

 ments with oats grown in sand dressed with phosphates, 

 potash, and lime. Treated pots watered once with the 

 mixed culture solution. Average weight per plant : un- 

 treated, 042 grm. ; treated, 0-74 grm. ; increase, 0'32 

 grm. = 76 per cent. Barley. — Field experiments on limed 

 plots of 484 square yards. Seed only treated with bacterial 

 culture. Yield per plot : untreated, 608 lb. ; treated, 

 6gi lb.; increase, 83 lb. = i3'6 per cent. The barley from 

 a treated plot also yielded a higher nitrogen content. 



Mgr. N. per cent. Weight of rooo corns Mgr. N. per corn 

 Untreated ... 1-55 ... 48-5 grms. ... 075 



Treated 176 ... 49'S .. •■• °'^7 



Bulbs. — Galtonia candicans grown in sandy soil, manured 

 and limed, 250 bulbs of equal size in each bed. Treated 

 bed watered twice with mixed culture solution. Weight 

 of bulbs when lifted and dried at end of season : untreated, 

 6q lb. 3 oz. ; treated, 82 lb. li oz. ; increase, 12 lb. 145 oz.= 

 i8-6 per cent. Parsnips. — Grown in garden soil, manured 

 and limed. Half the bed watered once with mixed culture 

 solution. Every parsnip grown in the bed included in the 

 weights. Untreated, 68 roots weighed 22 lb. 14 oz. ; 

 average per root = 5-38 oz. ; treated, 65 roots weighed 

 26 lb. 10 oz., average per root, 6-55 oz. ; increase per 

 root, 1-17 oz. = 21-7 per cent. In all the experiments the 

 soil was trealed with lime before the mixed culture was 

 applied. 



Royal Microscopical Society, April 21. — Mr. E. J. 



Spitta, vice-president, in the chair. — The recent and fossil 

 Foraminifcra of the shore sands of Selsey Bill, Sussex : 

 E. Heron-Allen and A. Earland. — The disappearance of 

 the nucleolus in mitosis : E. J. Sheppard. 



Physical Society, April 23. — Dr. C. Chree, F.R.S., 

 president, in the chair. — A want of symmetry shown by 

 secondary X-rays : Prof. W. H. Bragg and J. L. 

 Glasson. When a primary X-ray strikes an atom, a 

 secondary X-ray sometimes starts out from the place of 

 impact. The experiments described in the paper were made 

 with the object of comparing the intensity of emission 

 of the secondary X-ray in a direction making an angle 

 of about 45° with the primary with the intensity in a 

 direction making an angle of 135°, and therefore turning 

 back almost completely. It was found that in the case 

 of atoms of platinum, tin or aluminium, or of such light 

 atoms as are contained in celluloid, the former was larger 

 than the latter, being sometimes three times as great. 

 Madsen has obtained similar, but much greater, inequali- 

 ties in the case of the 7 rays. When atoms of copper or 

 iron were tested, atoms which give rise to a very soft 

 radiation, there was little inequality. A similar inequality 

 effect also occurs in the case of /3 rays. On the original 

 pulse theory, calculation showed that there should be no 

 inequality cf the secondary X-radiation in any case. If 

 that theory were abandoned, and the X-rays were supposed 

 to be bundles of energy travelling through space, there 

 did not appear to be sufficient definition of such entities 

 as would enable any comparison to be made between theory 

 and experiment. If the rays were supposed to be material 

 the facts were generally in agreement with expectation, 

 and afforded another instance of close parallelism between 

 the phenomena of the X and the y rays. — Transformations 

 of X-rays : C. A. Sadler. It has been shown that the 

 members of the group of metals chromium — silver emit 

 under suitable primary beams radiations which are homo- 

 geneous, and which increase in penetrating power with 

 increase of atomic weight of the radiator. Using these 

 homogeneous beams, the tertiary radiation excited by them 

 in other metals has been studied by the author. It was 

 found that the tertiary radiation excited in any member 

 of the group Cr — Ag was homogeneous, and its penetrating 

 power "was that characteristic of the radiation from the 

 substance when excited by a primary beam. With any 

 given tertiary radiator it was found that the intensity of 

 the homogeneous type of radiation emitted when the homo- 

 geneous radiations from the members of the group Cr — .\g 

 successively fell upon the radiator was inappreciable unless 



