Oct. 12, 1883.] 



♦ KNOWLEDGE ♦ 



225 



the intermediate districts. Still more clear does this con- 

 clusion become when the existing habitats are in islands or 

 peninsulas, when the animals themselves are clearly archaic 

 in type, and when the intermediate districts are actually- 

 inhabited by more advanced and distantly related 

 animals, like our own hedgehogs. Other isolated in- 

 sectivorous families are the golden moles, now confined 

 entirely to South Africa, and the potamogale, a pecu- 

 liar West African river shrew. Our own moles and 

 their kind are even more generally distributed than the 

 hedgehogs, being found in the northern half of both hemi- 

 spheres, though never spreading south of the equator ; and 

 they have clearly been preserved by their subterranean 

 habits, for which they have undergone such marked spe- 

 cialisation of structure and function. All these instances, 

 then, combine to show us that the insectivores are really a 

 decadent order, surviving for the most part only under two 

 sets of conditions — either in islands and peninsulas, far 

 from the fierce competition of the great continents ; or, if 

 on the continents, then under special circumstances of 

 life — nocturnal, subterranean, or aquatic — where they have 

 been spared the competition in its worse forms, or have 

 been endowed with special modes of defence by spines or 

 bristles, which enable them to hold their own somehow 

 against otherwise better adapted competitors. 



Of all the insectivores, however, the shrews are the 

 most central and least differentiated existing kind ; and 

 it is this fact which gives them their deepest claim to 

 respect in the eyes of the evolutionary naturalist. For the 

 insectivores themselves, as Professor Huxley has long in- 

 sisted, are, in many respects, the most central order in the 

 great division of mammals above the marsupials — the 

 Placentata of most modern authors. Hence we may say, 

 without exaggeration, that the shrew comes nearer than 

 any other existing animal to the prime ancestor of the 

 whole superior mammalian stock. There are many points, 

 indeed, in which some of the abnormal and very 

 archaic isolated insectivores strongly recall the mar- 

 supial type, and especially that of the phalangers. 

 Thus the shrews are by no means remotely related 

 on the one hand to the extremely ancient pouched animals, 

 the most primitive (geologically speaking) of all known 

 mammals ; while, on the other hand, the curious isolated 

 forms preserved for us in distant islands bridge over the 

 gap to the hedgehogs and the bangsrings, as well as, perhaps 

 in a less degree, to the carnivores, the lemurs, and the bats. 

 Thus, the shrews in particular, and the insectivores in 

 general, may be regarded as the great central junction of 

 the entire mammalian line, whence the various diverging 

 side-lines branch ofl' in ditierent directions towards all the 

 chief families and orders of mammals, up to the lions, the 

 elephants, the horses, the bats, the monkeys, and even man 

 himself. 



THE CHEMISTRY OF COOKERY. 



By W. Mattieu Williams. 

 XX. 



IN my last I described generally the dillusion of liquids;, 

 and the actions to which the names of endosmonis and 

 exosmosis have been given. It is easily seen that in ex- 

 tracting the juices of meat by immersion in water the work 

 is done by these two agencies. This is the case whether 

 the extraction is eHectcd by maceration (immersion in cold 

 water) or by stewing. 



Some of these juices, as already explained, exist between 

 the fibres of the meat, others are withiiA those fibres or 



cells, enveloped in the sheath or cell membrane. It is 

 evident that the loose or free juices will be extracted by 

 simple diflusion ; those enveloped in membianes by exos- 

 mosis through the membrane. The result must be the 

 same in both cases ; the meat will be permeated by the 

 water, and the surrounding water will be permeated by 

 the juices that originally existed within the meat. As 

 the rate of difTusion — other conditions being equal — is 

 proportionate to the extent of the surfaces of the diverse 

 liquids that are exposed to each other, and as the rate of 

 osmosis is similarly proportioned to the exposure of mem- 

 brane, it is evident that the cutting-up of the meat will 

 assist the extraction of its juices by the creation of fresh 

 surfaces ; hence the well-known advantage of mincing in 

 the making of beef-tea. 



It is interesting to observe the condition of lean meat 

 that has thus been minced and exposed for a few hours to 

 these actions l>y immersion in cold water. On removing 

 and straining such minced meat it will be found to have 

 lost its colour, and if it is now cooked it is insipid, and 

 even nauseous if eaten in any quantity. It has been 

 given to dogs and cats and pigs ; these, after eating a 

 little, refuse to take more, and when supplied with 

 this juiceless meat alone, they languish, become ema- 

 ciated, and die of starvation if the experiment is 

 continued. Experiments of this kind contributed to the 

 fallacious conclusions described in No. 6 of this series. 

 Although the meat from which the juices are thus com- 

 pletely extracted is quite worthless alone, and meat from 

 which they are partially extracted is nearly worthless alone, 

 either of them becomes valuable when eaten with the juices. 

 The stewed beef of the Frenchman would deserve the con- 

 tempt bestowed upon it by the prejudiced Englishman if it 

 were eaten as the Englishman eats his roast beef ,; but when 

 preceded by a potage containing the juices of the beef it is 

 quite as nutritious as if roasted, and more easily digested. 



Graham found that increase of temperature increased the 

 rate of diffusion of liquids, and in accordance with this the 

 extraction of the juices of meat is eflected more rapidly 

 by warm than by cold water, but there is a limit to this 

 advantage, as will be easily understood by referring back to 

 No. 3, in which is described the conditions of coagulation 

 of one of these juices — viz., the albumen, which at the tem- 

 perature of 134° Fahr. begins to show signs of losing its 

 fluidit}- ; at 1 G0° becomes a semi-opaque jelly ; and at the 

 boiling-point of water is a rather tough solid, which, if kept 

 at this temperature, shrinks, and becomes harder and harder, 

 tougher and tougher, till it attains a consistence comparable 

 to that of horn tempered with gutta-percha. 



I have spoken of beef-tea, or Extractum Carnis (Liebig's 

 Extract of Meat), as an extreme case of extracting the 

 juices of meat, and must now explain the difference 

 between this and the juices of an ordinary stew. Supposing 

 the juices of the meat to be extracted by maceration in 

 cold water, and the broth thus obtained to be heated in 

 order to alter its raw flavour, a scum will be seen to rise 

 upon the surface ; this is carefully removed in the manufac- 

 ture of Liebig's extract or the preparation of beef-tea for 

 an inxalid, but in thus skimming we remove a highly- 

 nutritious constituent — viz., the albumen, which has 

 coagulated during the heating. ^The pure beef -tea, 

 or Extractum Carnis, contains only the kreatine, krea- 

 tinine, the soluble phosphates, the lactic acid, and 

 other non-coagulable saline constituents, that are rather 

 stimulating than nutritious, and which, properly speaking, 

 are not digested at all — i.e., they are not converted into 

 chyme in the stomach, do not pass through the pylorus 

 into the duodenum, &c., but, instead of this, their dilute 

 solution passes like the water we drink directly into the 



