56 



NATURE 



[March 20, 19 19 



for legislation rather than for scientific investigation. 

 The chief insect pests in this country are the two grain- 

 weevils, Calandra granaria and C. oryzae, while in 

 India two other beetles, Rhizopertha dominica and 

 Trogoderma khapra, are also responsible for much 

 direct injury. Experiments on the rate of multiplication 

 of the weevils show that at suitable temperatures they 

 breed all the year round, but in this country normally 

 only in the warmer months. At about 28° C. a single 

 pair of rice-weevils increased about seven-hundred-fold 

 in four months. The accumulated excrement of the 

 weevils attracts moisture and promotes decomposition, 

 accompanied by the evolution of large quantities of 

 ammonia, and in this way the destruction com- 

 menced by the ravages of the insects is completed. 

 The process of heating is the result of enzymic action 

 in the wheat itself, sometimes inaccurately spoken of 

 as respiration, though fermentation would be a better 

 term, which increases with rise of temperature (up 

 to about 55° C.) and moisture content (Bailey and 

 Gurjar). In the eyes of the trade, heating ajipears 

 to be a much more serious danger than weevilling. 

 It is at present avoided by abundant ventilation, the 

 grain being turned over as soon as the temperature 

 becomes dangerously high, so as to cool it and carry 

 off moisture. 



As an effectual means of preventing damage from 

 all these sources, airtight storage should be resorted 

 to. Unfortunately, however, considerable doubt has 

 been thrown on the efficacy of this ancient method 

 by a widespread belief in the ability of weevils to 

 withstand such treatment. This belief rests entirely 

 upon inaccurate observations. Thus we find that tins 

 which are supposed to be hermetically sealed, and 

 look perfectly sound, are often leaky, as can easily 

 be shown by placing them in hot water, when air 

 bubbles out. Numerous experiments made at King's 

 College by the lecturer and his colleague, Mr. H. D. 

 Elkington, who is responsible more especially for the 

 chemical analyses, prove conclusively that all insects 

 present are more or less rapidly destroyed when | 

 weevilly wheat is sealed up in airtight receptacles 

 which it nearly fills. This method of treatment 

 destroys the weevils in all their stages, and is also 

 fatal at any rate to adult mites. The same treat- 

 ment also prevents the growth of moulds and the 

 process of heating. Two Dewar flasks, filled with 

 grain having a moisture content of 207 per cent., 

 were incubated at about 28° C. One was merely 

 plugged with cotton-wool and the other hermetically 

 sealed. In the former the temperature gradually rose 

 to 49-4° C, while in the latter it remained almost 

 stationary. The life of insects and moulds and the 

 process of heating alike depend upon the supply of 

 oxygen, and where this is cut off no damage from 

 these sources need be feared. 



It has been demonstrated experimentally, not only 

 that weevils require an abundant supply of oxygen, 

 but also that carbon dioxide, if present in sufficient 

 quantity, has a directly poisonous action upon them. 

 In pure, moist carbon dioxide they become motionless 

 in three minutes, and can remain in this condition for 

 as much as four days (at room temperature) without 

 losing the power of recovery. A mixture of carbon 

 dioxide with 20 per cent, of oxygen is far more fatal 

 than pure carbon dioxide. This is probably because, 

 in the absence of oxygen, their metabolism is more 

 or less completely suspended, so that the carbon 

 dioxide is unable to exercise its poisonous effect. In 

 a mixture of 56-4 per cent, nitrogen, 20-36 per cent, 

 oxygen, and 23-22 per cent, carbon dioxide weevils 

 became motionless in forty-three hours (at about 

 30° C), and after ninety-one hours' exposure, though 



NO. 2577, VOL. 103] 



19-09 per cent, of oxygen still remained, none revived 

 when supplied with ordinary air. 



When wheat is sealed up in a normal atmosphere 

 carbon dioxide accumulates naturally owing to the 

 so-called respiration of che grain, the rate of accumula- 

 tion depending upon temperature and moisture condi- 

 tions. At ordinary room temperature (July to Octo- 

 ber) in three months 300 grams of English wheat, 

 having a natural moisture-content of 15-9 per cent,, 

 gave off 586 milligrams of carbon dioxide, sufficient 

 to raise the percentage of that gas in the air in the 

 receptacle (which was nearly filled with wheat) to 

 18-13. If insects also be present, the carbon dioxide 

 accumulates more rapidly owing to the large amount 

 which they themselves give off. It thus appears that 

 in hermetically sealed granaries completely filled with 

 grain there should be no need for any artificial addi- 

 tion of carbon dioxide such as has sometimes been 

 recommended, and, indeed, actually made, for the pur- 

 pose of destroying weevils. Under proper conditions, 

 which ought to be experimentally determined on a 

 large scale, the grain must become self-protective 

 as regards weevilling, mildew, and heating, to say 

 nothing of rats and mice. Any damage which might 

 arise while the carbon dioxide was accumulating would 

 probably be negligible. 



The construction of airtight granaries or silos is a 

 problem for the engineer, but there seems to be no 

 Insuperable difficulty in the way. If such granaries 

 existed in the large wheat-growing countries the grain 

 might he completely sterilised as regards insect-life 

 bv storing for a suitable period before shipment, and 

 the very serious weevilling which often takes place on 

 board ship might be avoided. Moreover, it would be 

 possible to equalise shipments all the vear round and 

 avoid the rush to get the grain awav after harvest. 

 Airtight storage would also. In all probabllitv. afford 

 by far the best means of maintaining reserves' of grain 

 to meet emergencies such as war and failure of 

 crops. 



Further details have been, and will be, published 

 In the reports of the Grain Pests (War) Committee of 

 the Royal Society, under the auspices of whirb th'-cp 

 Investigations have been carried out. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge.— Mr. Joseph Barcroft, F.R.S., of King's 

 College, has been appointed reader in physiology; Mr 

 A. V. Hill, F.R.S., of King's College, University lec- 

 turer in physiology; and Dr. Hartridge, of King's 

 College, University lecturer in the physiology of the 

 senses. 



The adjudicators for the Adams prize have proposed 

 as the subject for the prize for the period 1919-20 

 "The Nature and Analysis of Optical Spectra." 



Liverpool. — Thie council of the University has 

 accepted with great regret Prof. Herdman's resigna- 

 tion as from September 30 next of the Derby chair 

 of natural history, which he has held since 1882. As 

 announced in Nature of February 27, Prof. Herd- 

 man will occupy the new chair of oceanography, with- 

 out salary, for a period of one year from October i 

 next, and this tenure will perhaps lessen the severity 

 of the wrench he must feel at severing his long pro- 

 fessorial connection with the University. He will be 

 greatly missed by the University staff and students, 

 but freedom from lectures and administrative duties 

 will give him much more time for research, to which 

 he proposes to devote his remaining working years. 



