August 1, 1889.] 



♦ KNOW^LEDGE ♦ 



2U1 



skins periodically, after each moult becoming larger and 

 darker. During the first year of its life the young (!ock. 

 roach changes its skin three times ; the first immediately 

 after hatching, the second a month later, and the third not 

 till the end of the year. There would appear to be seven 

 moults in all before the fully developed form is attained, 

 but after the first thi-ee these are made only annually. This, 

 at least, is the conclusion ai'rived at by Cornelius from 

 observations made on captive cockroaches ; but it may be 

 open to question whether the course would have been pre- 

 cisely the same under more natural conditions, and, unfor- 

 tunately, no other observations have been recorded on this 

 particular species. If, however, the above lesults represent 

 the usual state of things, cockroaches are certainly gifted 

 with extraordinary longevity, for their life evidently extends 

 over a period of at least five years. One is accustomed to 

 think of insects as ti'uly ephemeral creatures, and it is pro- 

 bable that the majority of them do not I'equii'e more than 

 a single twelvemonth to complete their cycle of existence; 

 where the preliminary stages occupy a longer time than this, 

 the species chiefly feed in concealment — as buried in the 

 ground, like the grubs of the cockchafer, or in solid wood, 

 like those of the stag-beetle. The experience of Sir John 

 Lubbock with his ants has, it is true, demonstrated that the 

 life of insects may, under favourable conditions, last much 

 longer than we should have expected. Some of his ants 

 lived with him upwards of eight years ; but these were in 

 their perfect condition all that time, and their early life and 

 periods of transformation and growth had been, as asual, 

 rapidly accomplished. Cockroaches, on the other hand, if 

 the above results are to be accepted, take a long time to 

 pass through their introductory stages, but we have no 

 evidence at all as to how long they live after becoming full- 

 grown. To so active an insect the dangers and possible 

 mischances of a long larval life would necessarily be very 

 numerous, and it is highly probable that great numbers of 

 them would never reach maturity at all. Be that as it 

 may, their swarms are still quite large enough for human 

 comfort. Further observations on their life history, how- 

 ever, are much to be desired, though no doubt difficult to 

 carry out. A closely allied species, Blatld garmanica, was 

 studied by Hummel with a very diffeient result, the genera- 

 tions being found to succeed one another with much greater 

 rapidity, and analogy suggests that P. orientalis, which is 

 similarly an active surface living insect, should run a 

 similai- course, and should, at any rate, complete its cycle of 

 changes more rapidly than sluggish grubs which live in 

 solitariness and concealment. 



{To he continued.) 



THE PRODUCTION OF SUGAR. 



By Waud Colduidoe, B.A. Cantab. 



E8TERDAY the formation of sugar by plants 

 was one of the mysteries of nature. 

 Chemists and botanists, whilst they knew 

 that ordinary chemical attractions must be 

 the cause, were yet completely in the dark 

 as to how these forces worked. Thoy 

 realised that plants stiu-ted with carbonic 

 acid and water, and from these waste pro- 

 ducts of animal existence biiilt up in somo unknown way 

 the complex compound, sugar. From the deadly choke- 

 damp to the luxury sugar was a great transformation. The 

 plants could thus build ; but men of science could not coiu- 

 prohend the process. 



To-day, as the result of somo brilliant resc;u-chcs, the 



explanation has been found. A simple compound, the 

 formation of which by the plant can be readily accounted 

 for, has been transformed into a sugar. To understand the 

 process, it must be realised that abundant evidence proves 

 that plants promote processes which are the opposites of 

 combustion or oxidation. Plants liberate oxygen from 

 its compounds, and absorb that with which it was previously 

 combined. They can liberate oxygen from so stable a com- 

 pound as carbonic acid, and in water find a source for the 

 hydrogen which is essential to their development. The 

 products which could thus be formed are, respectively, from 

 carbonic acid, the lower oxide of carbon and oxygen, from 

 water, the gases hydrogen and oxygen. Experiments have 

 .shown that under the influence of the silent electric dis- 

 charge, and even without it, carbon monoxide and hydrogen 

 combine to form a simple compound, formic aldehyde, 

 which is immediately connected with the formic acid of the 

 ant and of the stinging- nettle. So the changes which occur 

 in the plant under the combined influence of sunlight and 

 chlorophyl may be represented in symbols as follows : — 



CO, = CO 4- 

 Carbonic Carbonic + Oxygen 

 acid. oxide. 



CO + H., 



H,0 - H, + 



Water = Hydrogen + Oxygen. 



CH,0 

 Formic aldehyde. 



This formic aldehyde was the substance experimented on. 

 When it was suitably treated in the presence of the hydrate 

 of lime (Ca(HO);), it was induced to combine with itself 

 and to form another compound. The latter is composed of 

 the same ultimate indivisible particles (atoms) and in the 

 same proportions ; but they are now diSerently arranged 

 side by side, and with a larger number in the unit aggrega- 

 tion which chemists call molecules. This compound has 

 now been finally proved to contiun not one, but at least two 

 or three members of the family of substances, carbo- 

 hydrates, to which sugar belongs. Thus in our laboratories 

 Ciin now be imitated the process of which plants previously 

 held the secret. 



Whilst, however, the fact is marvellous that a sugar has 

 been obtained artificially, it must be remembered that the 

 process is absolutely uneconomical, for the yield Ls very 

 small. This remark too ajjplies to another process of 

 artificial production. The sweet viscid liquid, glycerin, and 

 its stinking, irritating offspring, acrolein, which gives the 

 nasty smell of burning fat, have both been transformed into 

 sugar; but the quantity obtained is very small in proportion 

 to the gl3-cerin or acrolein used. The importance of these 

 researches lies in the fact that they show how the chemical 

 changes which characterise the vital action of the plant can 

 be imitated with dead matter, and that further they shed a 

 bright gleam of Kght on the hitherto obscure question of the 

 arrangement of the indivisible particles, atoms, within the 

 compound particles, the molecules of these substances. 



Our sujjply of sugar will alwajs be drawn from the 

 vegetable kingdom, the synthetic laboratory of nature. 

 Many plants work hard and economically at the production 

 of sugar, and form it in quantity. It occurs in all piu'ts of 

 plants — root, stem, leaves, flower, fruit, and seed. In some 

 grasses it is very abundant, in the sugar-atne, in the Sorgho 

 grass, and in the young shoots of the maize. In the common 

 carrot and parsnip, and especially in the tleshy beet, large 

 quantities are contained. But for its commercial extrac- 

 tion two sources are chieUy used — the sugar-cane and the 

 beetroot, and a third is of growing importance, the Sorgho 

 grass. 



The sug;ir-cane has fur greater natural advantages than 

 the Ijeetroot. At one time the former held the field with- 

 out a rival. But during the Napoleonic wars, France was 

 ileprivod of her supjily of sugar, and she was driven to 



