ISO 



KNOWLEDGE 



[Dec. 23, 188^ 



imperfi'i-tly cookwl ; then comes the "tide «i fortune" to 

 the youuf; worms. For when the young worm lias l)een 

 .nten l«y the man, tlie 1 .ladder- tail drops off. Each little 

 liead and neek finding it.self in the human stomach, recog- 

 nises its lawful hubitat. Each atta-lies itself to the lining 

 niemlirane of the liunian intestines, and each l)y a process 

 of budding produces joint after joint, until man is pre- 

 sented witli his matured "guest" 



If we tjihulatv matters thus, the history of the tapeworm 

 will liecome clear: — 



l.t Epoch. 



f Stage 1. The egg derived from iiarcnt "| 



I tapeworm of man. I 



,, 2. Swallowed by the pig; do- | 

 ) veloping. l_ 



i„ 3. The " Resting Larva," or | 

 cystic worm, in tlic pig's I 

 musclee, and forming | 



Passed i 

 the 



2nd Epoch 



" measly" pork. J 



, 4. Swallowed by man. ~| 



I, 5. Development of the head and | ,,.,,• 



necK, and attachment to 1 ' "''*'^" '" 



,'..,. f man as 



man s inteetine. ' ii \ t 



I „ 6. The production by budding of | "" '""'^• 

 |_ the adult worm. J 



As a last piece of parasite biography, we may glance at 

 the history of a form which now and then attracts the 

 notice of even Imperial Parliament itself. This form is 

 tlie famous Trichina, which acquires an unenviable noto- 

 riety, in that it may, unlike the tapeworm race, cause the 

 death of its " host." Each trichina is a minute worm, 

 coiled, in its immature condition, within a little sack or 

 bag, which in numbers may be found again in the muscles 

 of the pig. Where the pig gets its trichinw fi-om is hardly 

 cei-tain, but rats are believed to be the sources of supjily 

 for the pig race. In the muscles of the pig each trichina 

 is, as already remarked, in an imperfect and youthful 

 condition. If the pig lives long enough, the trichina; will 

 disappear from its muscles, or will degenerate to become 

 mere specks of lime. But should a man eat a portion of 

 trichina-infected pork, the youthful worms will undergo, 

 in his digestive system, a rapid and extraordinary 

 development. The trichina; will develope enormous 

 numbers of young ; and the young lirood will now 

 naturally seek the muscles of man for a habitation, as their 

 parents before them sought those of the pig. Then ensues 

 the tug of war for the afflicted human. The paiu caused 

 by the boring of these microscopic worms from stomach to 

 muscles is intense. It is this pain and attendant symptoms 

 that constitute the disease known as trichiniasis. If the 

 patient's strength holds out, he is safe whenever the young 

 trichina-brood enter the muscles. There they rest, and re- 

 main to degenerate — unless, indeed, cannibal instincts were 

 represented in the human race ; in wliich case the cannibal 

 world experience n few of the tortures and trouliles which 

 are said proverbially to afllict the just and unjust alike. 



The great lesson to the learned, from om- survey of para- 

 sites, is care in the choice and increased care in the cook- 

 ing of our food. It .should be remembered that the germs 

 of these parasites are killed by a sufficiently long exposure 

 to heat. I[ence, whilst underdone meat may ha\e its 

 charms, it has likewise its gi-ave dangers. Pork, in any 

 and every fashion, should at all times be thoroughly cooked. 

 In this latter case, the parasitic horde may not merely be 

 destroyed, but m.ay even contribute in a microscopic way, 

 to human nutrition. 



Mb. S. L. JI. Barlow, one of the trustees of the Metropolitan 

 Museum of Art, New York, has presented to that institution, through 

 its director, Oenornl di Cesnoln, a collection of vnscs lately discovered 



SOLIDS, LIQUIDS, AND GASES. 



By W. >r.\TTiEU Williams. 

 PAKT V. 



AS already .stated, in Part .'5 of this .series, page Ht^, tJic 

 conversion of water into steam under ordinary atmo- 

 spheric pressure demands 9GGG° of heat over and above 

 that which does the work of raising the water to '212'^, or, 

 otherwise stated, as much heat is at work in a given weight 

 of steam at 212°, as would rai.se the same quantity of 

 water to 1,178'6'' if it remained liquid. 



James Watt concluded from his experiments tliat a given 

 weight of steam, whatever may )>e its density, or, in other 

 words, under whatever pressure it may exist, contains the 

 same quantity of heat According to this, if we reduced 

 the pressure sufficiently to bring down the boiling point to 

 112°, instead of 212", the latent heat of the steam thus 

 formed would be 1,0GCG° instead of 966 'G', or if, on the 

 other hand, we placed it under sufficient pressure to raise the 

 boiling point to .'? 1 2", the latent heat of the steam would be re- 

 duced to 8G6G°, i.e., only 8G6'6° more would be required to 

 convert the water into steam. If the lioiling point were 

 412°, as it is between 19 and 20 atmospheres of pressure, 

 only 7G6'6° more heat would be required, and so on, till wi- 

 reach a pressure which raises the boiling point to 1,1786^, 

 when the water would become stetm without further heating, 

 i.e., the critical point would be reached, and thus, if Watt 

 is right, we can easily determine, theoretically, the critical 

 temperature of water.* 



Mr. Perkins, who made some remarkable experiments 

 upon very high pressure steam many years ago, and ex- 

 hibited a steam guu at the Adelaide Gallery, stated that 

 red-hot water does not boil ; that if the generator be suffi- 

 ciently strong to stand a pressure of 60,000 lb. load on the 

 safety valve, the water may be made to exei-t a pressure of 

 56,000 lb. on the square inch at a cherry red-heat without 

 boiling. He made a number of rather dangerous experi- 

 ments in thus raising water to a red-heat, and his assertion 

 that red-hot water does not boil is curious when viewed in 

 connection with Dr. Andrew's experiments. 



I cannot tell how he arrived at this conclusion, having 

 been unable to obtain the original record of his experiments, 

 and only quote the above second-hand. It is worthy of 

 remark that the temperature he names is aliout 1,170^, or 

 that which, if Watt is right, must lie the critical tempera- 

 ture of the water. Perkins' red-hot water would not boil, 

 as he states, being then in the intermediate condition. 



So far, we have a nice little theory, which not only shows 

 how the critical state of water must be reached, but also 

 its precise temperature ; but all this is based on the assump- 

 tion that "Watt made no mistake. Unfortimately for the 

 simplicity of this theory, Regnault states that /(i.< experi- 

 ments contradict those of Watt, and pro\ e that the latent 

 heat of steam does not diminish just in the same degi-ee as 

 the boiling-point is i-aised, but that instead of this the 

 diminution of the latent heat progi'esses 30^ per cent, more 

 slowly than the rise of temperature, so that, instead of the 

 latent heat of steam between boiling-points of 212" and 

 312^ falling from 966 6° to 866 6° it would only fall to 

 895-1° or 69-5° for every 100°. 



If this is correct, the temperature at which the latent 

 heat of steam is reduced to zero is much higher than 1,178"6° 

 and is, in fact, a continually receding quantity never abso- 

 lutely reached ; but I am not prepared to accept these 

 figures of Regnault as implicitly as is now done in text 



• Watt's own figure f»r the latent heat of steam at 212° was 950* 



