98 



♦ KNOWLEDGE ♦ 



[Aug. 17, 1883, 



the genealogy of so isolated and divergent a group as the 

 rodents. South America is a iperfect mine of antiquated 

 types, living or extinct ; its long separation from the rest 

 of the world, before the restoration of communications viA 

 the Isthmus of Panama, made it a Kort of rival to Australia 

 and the Cape of Good Hope as an area for the preservation 

 of early forms, superseded elsewhere by the higher moditi- 

 cations which result from the fiercer competition and 

 hardei- struggle for life in the great continents. In the 

 pliocene deposits of La Plata, accordingly, there occur the 

 bones of a singular early creature, a missing link in the 

 ■way of a rodent, which helps to bridge over the gap to the 

 main line of mammalian development. This most primitive 

 known type of rodent (most primitive in organisation, I mean, 

 for we have true squirrels and other perfect rodents much 

 earlier in time) is known as Mesotlierium (or Intermediate 

 Beast), and has four incisors in its lower jaw. The second 

 pair are smaller than the first, and are placed behind them ; 

 and in some other dental peculiarities this stranded type 

 more nearly approaches the ordinary central form of 

 mammals. In particular, the great incisors themselves 

 are blunter and far less characteristically rodent-like than 

 in all the existing species. Now, it is quite clear that 

 the raison d'etre of the rodents as a group, the funda- 

 mental diflerence upon which all their other class-diifer- 

 ences depend, is the peculiar nature of their teeth ; so 

 that in this isolated South American form we have, so to 

 speak, a central mammalian type in the very act of grow- 

 ing into a true rodent. In many ways Mesotherium recalls 

 the hoofed animals, and especially thataberrant little Syrian 

 creature, the so-called coney, the last survivor of an order 

 now otherwise quite extinct. There are other points in which 

 it resembles those other archaic South American mammals, 

 the sloths and armadillos ; and altogether we may consider 

 it as a late lingering form of a very primitive rodent type, 

 preserved in the once insular Neotropical region long after 

 all its kind had been lived down elsewhere by the more 

 advanced and perfected true rodents. Thus, we may fairly 

 conclude that the ancestors of squirrels and rabbits pro- 

 bably started from a type hardly superior in organisation 

 to the Australian marsupials, and linked on either hand to 

 the hoofed animals and to the edentates ; that they gra- 

 dually lost the two useless incisors in either jaw, except in 

 the case of the hare and rabbit section, which still retains 

 one pair in a rudimentary condition ; and that at the same 

 time they gradually modified the remaining and functional 

 pair in adaptation to their special habits, till at last they 

 grew into the very long and efficient, sharp, cutting tools 

 with whose appearance we are so familiar in the case of the 

 rabbit, the mouse, and the squirrel. 



THE CHEMISTRY OF COOKERY. 



XV. 



By W. Mattieu Williams. 



A CORRESPONDENT of Manchester asks me which 

 is the most nutritious, a slice of English beef 

 in its own gravy, or the browned morsel as served in an 

 Italian restaurant with the burnt sugar addition to the 

 gravy '! 



This is a very fair question and not difficult to answer. If 

 both are equally cooked, neither over-done nor under-done, 

 they must contain weight for weight exactly the same con- 

 stituents in equally digestible form, so far as chemical 

 composition is concerned. Whether they will actually be 

 digested with equal facility and assimilated with equal 



completeness depends upon something else not measurable 

 by chemical analysis, viz., the relish with which they are 

 respectively eaten. To some persons the undisguised 

 fleshiness of the English slice, especially if underdone, is 

 very repugnant. To these the corresponding morsel, cooked 

 according to Francatelli rather than Mrs. Beeton, would 

 be more nutritious. To the carnivorous John Bull, who 

 regards such dishes as " nasty French messes," of question- 

 able composition, the slice of unmistakable ox flesh, from 

 a visible joint, would obtain all the advantages of apprecia- 

 tive mastication and that sympathy between the brain and 

 the stomach, which is so powerful, that when discordantly 

 exerted may produce the ettects that are recorded in the 

 case of the sporting traveller, who was invited by a Red 

 Indian chief to a " dog-fight," and ate with relish the 

 savoury dishes at what he supposed to be a preliminary 

 banquet. Digestion was tranquilly and healthfully pro- 

 ceeding, under the soothing influence of the calumet, when 

 he asked the chief when the fight would commence. On 

 being told that it was over, and that in the final ragout he 

 had praised so highly the last puppy-dog possessed by the 

 tribe had been cooked in his honour, the normal course of 

 digestion of the honoured guest was completely reversed. 



Reverting to the fat used in frying, and the necessity of 

 its purification, I may illustrate the principle on which it 

 should be conducted by describing the method adopted in 

 the refining of mineral oils, such as petroleum or the 

 paraffin distillates of bituminous shales. These are dark, 

 tarry liquids of treacle like consistency, with a strong 

 and offensive odour. Nevertheless they are, at but little 

 cost, converted into the " crystal oil " used for lamps, and 

 that beautiful pearly substance, the solid, translucent 

 paraffin now so largely used in the manufacture of candles. 

 Besides these, we obtain from the same dirty source an 

 intermediate substance, the well-known " Vaseline," now 

 becoming the basis of most of the ointments of the pharma- 

 copceia. This purification is effected by agitation with sul- 

 phuric acid, which partly carbonises and partly combines 

 with the impurities, and separates them in the form of a 

 foul and acrid black mess, known technically as "acid tar." 

 When I was engaged in the distillation of cannel and 

 shale in Flintshire, this acid tar was a terrible bugbeai'. It 

 found its way mysteriously into the Alyn river, and 

 poisoned the trout ; but now, if I am correctly informed, 

 the Scotch manufacturers have turned it to profitable 

 account. 



Animal fat and vegetable oils are similarly purified. 

 Very objectionable refuse fat of various kinds is thus made 

 into tallow, or material for the soap-maker, and grease for 

 lubricating machinery. Unsavoury stories have been told 

 about the manufacture of butter from Thames mud or 

 the nodules of fat that are gathered therefrom by the mad- 

 larks, but they are all false. It may Vie possible to purify 

 fatty matter from the foulest of admixtures, and do this so 

 completely as to produce a soft, tasteless fat, i.e., a butter 

 substitute, but such a curiosity would cost more than half- 

 a-crown per pound, and therefore the market is safe, espe- 

 cially as the degree of purification required for soap-making 

 and machinerj' grease costs but little, and the demand for 

 such fat is very great. 



These methods of purification are not available in the 

 kitchen, as oil of vitriol is a vicious compound. During 

 the siege of Paris some of the Academicians devoted them- 

 selves very earnestly to the subject of the purification of fat 

 in order to produce what they termed " siege butter " from 

 the refuse of slaughter-houses, ic, and edible salad oils 

 from crude colza oil, the rancid fish oils used by the 

 leather-dresser, ic. Those who are specially interested in 

 the subject may find some curious papers in the Comptes 



