322 



SCIENTIFIC NEWS. 



[April 6, I? 



the laboratory do to penetrate the secret changes which 

 turn these black specks into wriggling tadpoles ? The 

 thorough study of the development of the tadpole is, we 

 must admit, far from easy ; but some of the most inter- 

 esting points can be made out even by a novice. If a 

 mass of spawn just laid can be captured, the segmenta- 

 tion of the eggs may be observed. The surest way is to 

 catch and keep a female with an attached male ; but close 

 observation from day to day of a particular pond or 

 ditch will enable us to find a bunch of newly-laid spawn. 

 Place a few of the eggs in a watch-glass filled with water 

 and blackened on the outside by a coat of varnish. The 

 cleavage of the egg into two, four, eight, and more cells 

 may then be observed from hour to hour with a simple 

 lens. 



Any child who keeps a glass jar with frog-spawn in it 

 can see the slow change of the round egg into the tailed 

 larva ; but the careful study of the very young tadpole 

 requires some knowledge, besides skill in the use of 

 instruments. We pass on to a later stage, where even 

 the untrained observer can find something to do. In 

 early summer active tadpoles, with long tails and a tiny 

 rudiment of hind legs, can easily be found. Capture 

 some of these, and kill them by placing in hot water, 

 about as hot as the hand can bear. The little creatures, 

 only about an inch long and very tender, have to be dis- 

 sected, and this requires some management. But first 

 go over the outside of the body with a lens. Notice 

 the tail, the hind legs, the rounded and swollen 

 body, the mouth and the eyes. Then secure the tad- 

 pole in a convenient position — that is, back downwards. 



A pomatum-pot or any similar vessel must be filled, 

 while hot, with solid paraffin, obtained by melting a bit 

 of candle. When the paraffin is hard, take up the 

 tadpole with the point of a knife, dry it for a moment 

 with blotting paper, and lower it upon a part of the sur- 

 face of the wax which has been melted for a moment 

 with a hot rod or wire. With some dexterity, but pro- 

 bably not at the very first trial, the tadpole can be 

 secured in this way. If alcohol is at hand, it is a good 

 plan to dip the tadpole in it before drying and mounting, 

 as a trace ot alcohol does not repel the melted wax so 

 effectually as water. The next thing is to remove the 

 skin from the exposed surface of the body. A pair of 

 needles in clever hands can be made to do the work, but 

 insect-forceps and fine, sharp scissors are much better. 

 The pomatum-pot should be placed in a larger dish, and 

 water added till the tadpole is just covered. Gradually 

 cut or tear open the body, and then study with a lens the 

 parts exposed. Our figure will show what is to be seen 

 in a successful preparation. Among the points to be 

 made out are the fore limbs, which were not visible be- 

 fore dissection, being concealed beneath a fold of skin 

 and muscle (the opercular fold), from which they protrude 

 only in a late stage of tadpole life. The gills in this 

 stage are internal only, the external gills seen in very 

 young tadpoles having been absorbed. It is to be re- 

 marked that lungs co-exist with these gills ; but they are 

 destined for future use only, and have never yet been 

 filled with air. The long intestine is well-suited to the 

 vegetarian diet of the tadpole. As the carnivorous 

 appetite grows, the intestine becomes shorter and simpler. 

 It is of interest to observe the reversal of the complicated 

 spiral into which the closely-wound intestine is thrown. 

 The arrangement is often compared to a watch-spring, 

 and has been so figured. (See, for example, Owen's 

 " Comp. Anat. of Vertebrates," vol. i., p, 624.) A descrip- 



tion so imperfect passes overa curious mechanical adapta- 

 tion. The tadpole's intestine is at first straight, and no 

 longer than the body. Then it gradually lengthens, and 

 coming greatly to exceed the length of the body, must be 

 thrown into many coils. It is well known that to wind 

 in a regular and continuous spiral a tube which is 

 attached at both ends would twist and strain its walls ; 

 but, by reversing the spiral during half of its extent, the 

 twist is taken of!'. Our readers will perhaps recollect in 

 this connection Mr. Darwin's account of the tendril of 

 the bryony. 



If the mouth be dissected, we discover the horny 

 plates which enable the tadpole to crush the green 

 weeds upon which it lives. In front are the plates which 

 form the beak. The upper plate is the larger, and comes 

 down in front of the lower. Behind these are rows of 

 smaller horny teeth on the sides of the mouth. The 

 edges of the lips are divided into many-rounded papilla. 

 The horny teeth completely disappear during transforma- 

 tion, and are succeeded by calcified teeth with a quite 

 different arrangement. 



MAKING PIG IRON WITH GAS. 



'T'HE American Manufacturer says that Mr. Jacob T. 

 Wainwright, a well-known metallurgical engineer, 

 of Pittsburg, Pa., has succeeded in making pig iron with 

 natural gas as fuel. His furnace differs from the ordi- 

 nary blast-furnace in this, that, while dispensing with 

 coke, it has overcome the great difficulty noted in con- 

 nection with other experiments in gas-furnaces, by a 

 mechanical device for supporting the burden. This 

 device consists of a series of pipes covered with fire-clay 

 tiles, and at the same time ventilating the pipes with a 

 current of air. A combustion-chamber is also connected 

 with the furnace, which reduces the amount of gas needed 

 to produce the required heat, and also prevents the 

 chilling of the furnace, which has been a great obstacle 

 to the success of other experiments. 



In the new furnace the ordinary cupola blower is used, 

 and the gas and air are introduced in a very simple 

 manner into the combustion-chamber in a separate pipe. 

 The current for cooling the tubes, already mentioned, is 

 supphed from the same air blast, and from thence may 

 be utilised in the furnace. Ordinary cupolas may be 

 easily altered, so as to do the required work, by adding 

 the combustion-chamber and the protecting tubes for 

 supporting the burden. 



The tests were made at the iron and lead works of 

 William G. Price, on Price Street, where the inventor 

 had the hearty co-operation of the manager, Mr. David 

 Carlin. Mr. Carlin says that the furnace worked rapidly, 

 and that its success is no longer doubtful. 



— — >-^a^>^fe-» — 



The Cobra Poison. — In spite ol numerous investiga- 

 tions carried on in India and elsewhere, there still exists 

 the greatest uncertainty as regards the chemical nature 

 of the venom of the cobra. Until this is known, it will, 

 of course, be almost impossible to find an antidote. 

 According to the latest hypothesis put forth by R. N. 

 Wolfenden, the poisonous ingredient belongs to the pro- 

 teine group of bodies ; he finds in it globuline, syntonine, 

 and serum-albumen. It is a curious fact that the chemi- 

 cal nature of animal poisons (spiders, snakes, fish, etc.) 

 has not yet been determined in any case. — Monthly Maga- 

 zine of Pharmacy. 



