SCIENCE. 



577 



to finding the difference of density between two mixtures 

 of alcohol and water of different strengths. It was found 

 that pure butter, at 15° C, would remain in equilibrium 

 in alcohol of 53.7 per cent. This corresponds to specific 

 gravity 0.926. This butter was obtained from a gentle- 

 man, at whose country place the bufer was made. I 

 obtained oleomargarine trom melted warm beef suet by 

 pressure. At a temperature of 25 C, this expressed fat 

 had the consistency of butter. The alcohol which at 15 

 C, would hold it in equilibrium had a strength of 59.2 per 

 cent., which corresponds to a specific gravity of 0.915. 



The question of the possibility of distinguishing butter 

 from oleomargarine becomes equivalent to the possibility 

 of distinguishing alcohol of 53.7 per cent., from alcohol of 

 59. 2 per cent. As this difference is 5.5 degrees of Gay 

 Lussac's alcohometer, it is very evide.it that the specific 

 gravity is a sufficient character for distinguishing butter 

 from oleomargarine. This difference may appear more 

 clearly to persons not familiar with alcohometry by stat- 

 ing that it is the difference between 0.926 specific gravity 

 and 0.915. 



By means of the tables of Gay Lussac and of Tralles,* 

 it is a very easy matter to prepare alcohol of the required 

 strength at any temperature, to be kept in bottles fcr 

 future use. 



As the expansion of fats is different from that of alcohol, 

 it is advisable to bring the alcohol to 1 5° C, when making 

 an observation, which can be easily done by any one pro- 

 vided with a thermometer. 



To deliver the sample of fat on the alcohol, I have found 

 that the best plan is to melt the fat and let a large drop 

 of it fall into the f'quid. The fat should be melted in a 

 little spoon or a little scoop, and the drop should be de- 

 livered by bringing the spoon or scoop close to the surface 

 of the alcohol. It requires a little practice to do this neat- 

 ly, so as not to get an air bubble in the ball of melted fat. 

 When an air bubble becomes imprisoned in the fat, I have 

 had no difficulty in removing it with a strip of paper, 

 while it lies on top of the alcohol. Sometimes the globule 

 of fat only partially sinks in the alcohol ; the top of it be- 

 comes, flat and remains exposed above the liquid. A 

 slight tap on the side of the glass is then generally suf- 

 ficient to form a wave and sink the globule. 



If we take alcohol of 56^ per cent., which represents 

 equal volumes of alcohol of 53.7 per cent., and of 59.2 per 

 cent., and if we deliver on the surface of this alcohol a 

 globule of melted butter and one of oleomargarine, the 

 butte/ will sink to the bottom and the oleomargarine will 

 remain at the top, while the two globules are still warm 

 and liquid. Afterwards, if the alcohol has a temperature 

 ot about 30° C, the butter will become solid, while the 

 oleomargarine may still remain liquid. Then the butter 

 will rise to the top of the alcohol, which is due to the ex- 

 pansion of butter on solidifying. If the alcohol be 

 then kept for a few minutes, at 15 C, the oleomargarine 

 will become opaque and remain at tne top while the solid 

 globule of butter will sink to the bottom. 



If instead of taking alcohol of 56 per cent, we use alco- 

 hol of 59.2 per cent., oleomargarine will remain on top and 

 butter will sink to the bottom at all temperatures above 

 \S° At 15 C, oleomargarine will remain ineqi- 

 librium in any portion of the liquid in which it may be 

 placed. 



If oleomargarine was always sold pure, the foregoing 

 indications would be sufficient to distinguish it from but- 

 ter, but the oleomargarine found in the market is always 

 more or less mixed with true butter to improve its taste 

 and appearance. This being the case, alcohol of 59 per 

 cent, is not the proper liquid to detect oleomargarine. We 

 should use alcohol of 55 per cent, and consideras oleomar- 

 garine any so called butter which will not sink to the bot- 

 tom in alcohol of this strength at 1 5 C. This is founded 

 on the fact that not more than ^ of butter is ever mixed 

 with oleomargarine to improve its taste and appearance. 

 *See the excellent tables of Prof. Mc. Culloh. 



Bearing in mind the experiments of Messrs. Leune and 

 Harburet, already cited, the proportion of butter and of 

 oleomargarine in a mixture could be easily detected by 

 finding what strength of alcohol will hold in equilibrium 

 at 1 5 C, a globule of fat under examination. As the dif- 

 ference of 59.2 and 53.7 is 5. 5, the proportion of oleomar- 

 garine is the difference between the strength of the alcohol 

 and 53.7, divided by 5.5, or more conveniently multiplied 

 by 0.18. If the alcohol required to hold a globule of fat in 

 equilibrium at 15 C, has a strength of 57 per cent., then: 

 ( 57 — 53-7 ) xo - I 8=3-3 x 0.18=5.95, or say of oleomar- 

 garine. If the alcohol had a strength of 58, then 58 — 53.7 

 x 0.18=4.3 x 0.1 8=7.72, or about -fc of oleomargarine. 



The proportions of butter and oleomargarine in a mix- 

 ture may be also determined without the aid of an alco- 

 hometer, by using the two solutions of 53.7 per cent, and 

 of 59.2 per cent. These may be placed in graduated 

 glasses and poured cautiously into a third glass, until an 

 alcohol of sufficient strength is obtained to keep in equi- 

 librium a globule of the fat under examination at 15 C. 



The relative volumes of the two solutions used in mak- 

 ing the mixture, give the proportions of butter and oleo- 

 margarine. 



The accuracy of these calculations rests entirely on the 

 results obtained by Messrs. Leune and Harburet. I have 

 not verified them by experiment, and I do not clearly see 

 their utility. When we buy butter it is interesting to 

 know whether what we buy is pure butter or not. It is 

 no palliation to the offence of selling oleomargarine for 

 butter that the oleomargarine contains { or £ of real but- 

 ter. 



FILARIA OF THE HUMAN BLOOD. 



The members of the Pathological Society, of London, 

 recently enjoyed the rare opportunity (in this country) of 

 seeing the filaria sanguinis hominis in the living state 

 from a patient in the London Hospital suffering from 

 hasmato-chyluria, under the care of Dr. Stephen Mac- 

 kenzie. They were also enabled to hear from Drs. 

 Cobbold and Vandyke Carter the facts at present known 

 concerning filarious disease, whilst the observations re- 

 lated by Dr. Mackenzie, most patiently and carefully 

 pursued for two months upon the case in question, were 

 a valuable addition to these facts. In one important 

 point these observations have resulted in a further dis- 

 covery, to which we shall refer again. Our present pur- 

 pose will be simply to gather up briefly the facts as 

 detailed by these speakers, and to indicate their bearings 

 upon the pathology of the obscure affections of the 

 lymphatic system with which they are connected. In 

 the first place we have now — thanks to the discoveries ot 

 Bancroft, Lewis, and Manson —a complete knowledge of 

 the life history of the parasite. Like so many similar 

 creatures, it presents us with an example of alternation of 

 generations ; or more correctly speaking, of the need of 

 two hosts for its full development. The minute almost 

 structureless worms found in the blood of the human 

 subject in such vast numbers are the embryonic forms of 

 the filaria which requires the mosquito in which to deve- 

 lop into the sexually mature worrn. The mosquito feed- 

 ing on the blood at night, when the filarial are generally 

 alone to be found, becomes gorged with them. Their 

 growth in the mosquito has been traced by Lewis and 

 Manson, and it is presumed that they are only liberated 

 from the body of their host by its death in the water to 

 which it always finally resorts. The nematoid is thus 

 set free, and possibly undergoes further development; for 

 the mature worm measures some three inches in length. 

 Its passage into the human body is easily explained; and 

 the analogy in this respect with the larger nematoid — the 

 guinea-worm— is one which Dr. Vandyke Carter ably 

 illustrated. Once within the human body, the worm 

 lodges in the tissues, but as to its migrations, and, in- 

 deed, its ultimate resting-place, but little is known. It 



