Mabch 1, 1898.] 



KNOWLEDGE. 



53 



recorded from the London district — July 18th, 1878 — when 

 I was fortunate in capturing a fine female specimen as it 

 hovered about the face of a sandbank on Ilampstead 

 Heath. Ptixi/iioda Itirti/iis is intensely fond of composite 

 llowers of the dandelion type, among the petals of which 

 it buries itself as it rilles the flower of its nectar and yellow 

 pollen, with which it becomes heavily laden. Its immense 

 bushy hind legs look like bright yellow bottle brushes. 

 The shape of the 

 hairs on the third 

 pair of legs is unique 

 among bees, each 

 tiny little branch 

 being surmounted 

 by a knob or club. 

 This bee is plenti- 

 ful along the south 

 coast. I found them 

 just emerging from 

 their burrows in the 

 sand at Littlehamp- 

 ton. Fig. i shows 

 the peculiar shape 

 of the tongue and 

 maxillae. 



Paimrijus is the nest in order. In colour it is a smoky 

 black. It is fond of making its burrows in hard paths, 

 and in such situations I have found them at Woking and 

 Hampstead, besides having swept them up from flowers 

 of the mouse-ear hawkweed, which used to flourish on 

 Hampatead Heath. 



The genus Nomadii consists of a number of species, more 

 like wasps than bees, with bright yellow-banded bodies. 

 All are cuckoo bees, depositing their eggs in the burrows 

 of AndrenidcB at the time when the rightful owners are 

 engaged storing up pollen for their progeny, which are 

 starved out by the stronger larvae of this cuckoo bee. The 

 tongue is a very neat one, more resembling that of the 

 honey bee {see Fig. 5). 



The prettily marked bee Epeolus raiieijutus is parasitic in 

 the cells of Colletes Darii'sana. It has a particularly sharp 

 sting. {To be coHtiinwd,) 



FlO. 5. — Namada succincta. 



THE VINEGAR EEL. 



By C. AiNSWORTH MiTCUELL, B.A,, F.I.C. 



IN the " Philosophical Essays " of Eobert Boyle, 

 published in 1661, there occurs the following 

 paragraph ; — " We have made mention to you of 

 a great store of living creatures which we have 

 observed in vinegar ; of the truth of which observa- 

 tion we can produce divers and severe witnesses, who 

 were not to be convinced of it until we had satisfied them 

 by ocular demonstration ; and yet there are divers parcels 

 of excellent vinegar wherein you may in vain seek for 

 these living creatures, and we are now distilling some of 

 that liquor, wherein we can neither by candle-light nor by 

 daylight discern any of these little creatures, of which we 

 have often seen swarms in other vinegars." 



This appears to be the earliest reference in scientific 

 literatiKe to the Leptodcra oxopliihi, which, from its shape 

 and fondness for vinegar, has long been known as the 

 "vinegar eel," and which in Schneider's opinion is iden- 

 tical with the " eels " which may often be observed in 

 sour paste. 



It is of very frequent occurrence in certain vinegar 

 works, more especially on the Continent, where the 



vinegar is manufactured at a lower and (for the eels) 

 more favourable temperature than is usual in England. 

 As to its origin, nothmg is definitely known, though 

 Czernat is inclined to think that it is introduced in the 

 water used for brewing the vinegar. Occasionally, on 

 allowing vinegar to stand exposed to the air for several 

 days in warm weather, it will soon be swarming with 

 these minute creatures, which have probably developed 

 from germs already present in the liquid. As wiU be 

 seen from the figure, which shows a single vinegar eel 

 under a high power, it is of very simple construction. 



The body is cylindrical and ends in a sharp point, and 

 the skin (which is changed from time to time) is smooth, 

 structureless, and very strong. According to Czemat's 

 average measurements, the length of the male's body is 

 about one twenty-fifth of an inch, that of the female one 

 sixteenth of an inch, the relative proportion generally being 

 as 1 : 1-3. In both sexes minute corpuscles may be 

 observed, which are put in motion by the contraction of 

 the body. In the female the eggs lie in two tubes which 

 unite in one opening. 



Vinegar eels are capable of moving either backwards or 

 forwards, and progress by alternately shaping themselves 

 iiito an S and straightening out again. They appear to be 

 incessantly darting through the vinegar at the top of their 

 speed in all directions, but always with a tendency towards 

 the surface, as they are air-breathing animals. Czernat 

 states that they never rest day or night, and that their rate 

 of progress is about one inch in twelve and a-half seconds. 



They are capable of living in very dilute alcohol or 

 acetic acid as well as in vinegar, and can withstand a 



The Vinegar Eel (higlily magnified). (After Pasteur.) 



great variation of temperature, not being killed until the 

 temperature reaches one himdred and forty degrees to one 

 hundred and fifty degrees Fahrenheit in one direction, and 

 about ten degrees below the freezing point of water in the 

 other. 



Pasteur was the first to point out how harmful the 

 vinegar eel is in the manufacture of vinegar. Vinegar is 

 prepared by causing certain micro-organisms (of which there 

 are several species classified under tbe term of "acetic 

 bacteria ") to act upon a liquid containing a small percentage 

 of alcohol, such as beer, fermented malt extract, or cider. 



By the action of these bacteria, which are supplied with 

 the requisite amount of atmospheric oxygen, the alcohol 

 is gradually converted into acetic acid, the process being 

 accelerated by maintaining a temperature of about one 

 hundred degrees Fahrenheit within the "acetifier." 



When insufficient- air is supplied, the bacteria form them- 

 selves into a slimy layer on the surface of the liquid, 

 popularly known as "mother of vinegar." Should, now, 

 vinegar eels develop in vinegar iu the course of manufacture, 

 they multiply rapidly, and a struggle for the air supplied to 

 the apparatus commences between them and the bacteria. 

 For some time a working balance may be struck between 



