October 21, 1922] 



NA TURE 



54: 



Vegetable Rennet. 



I have been endeavouring to make a list of plants — ■ 

 leaves, flowers, seeds, etc. — used in various countries 

 for coagulating milk in place of rennet, obtained from 

 the stomachs of young animals ; and I shall be glad 

 to learn of any additions that might be made to the 

 following list : — Galium verum, Withania coagulans, 

 Ficus Carica, Cynara cardunculus, Cynara scolymus, 

 Carduus nutans, Cnicus benedictus, Drosera peltata, 

 Datura Stramonium, Pisum sativum, Lupinus hirsutus, 

 Ricinus hirsutus, Pinguictda vulgaris, Leucas cepha- 

 lotes, Crotalaria Burhia, Rhazya stricta and Streblus 

 asper. 



With regard to some of the plants named above, 

 I would note that the references are not very clear as 

 to their use for milk coagulation. Any information 

 as to plants used in former days or at the present 

 time would be welcome and useful. A Hindu, also 

 an orthodox Jew, cannot touch, I understand, a milk 

 product that has been coagulated by rennet obtained 

 from a calf's stomach, and must therefore use a 

 vegetable coagulant ; and I believe that there are 

 other races in other parts of the world which use 

 vegetable coagulants. So far as I am aware, an 

 approximately complete list of plants used in various 

 parts of the world for coagulating milk does not exist, 

 and where a reference is found, details given are 

 scanty as to part of plant used, its preparation, and 

 method of use. R. Hedger Wallace. 



4 East Grove, Cardiff, September 20. 



A Question of Nomenclature. 



In his notice of Mr. S. Q. Hayes's " Switching 

 Equipment for Power Control " in Nature of 

 September 16, p. 374, your reviewer, commenting on 

 current Americanese, says : " Electrical engineers 

 talked about ' omnibus bars ' thirty years ago, it then 

 became ' bus bars,' and now apparently it has become 

 ' busses.' " Webster, who may be considered as 

 an authority on the language of that great nation, 

 defines a buss as "a kiss ; a rude or playful kiss ; a 

 smack," and quotes Herrick to the effect that : 

 Kissing and bussing differ both in this, 

 We buss our wantons, but our wives we kiss. 



So that although in both " bus bars " and " busses " 

 there is intimate contact and at times electricity 

 passes, it can scarcely be said that the two terms are 

 synonymous. Nor can it be said that the introduction 

 of such terms into electrical engineering is to be 

 commended. F. H. Masters. 



Capillarity. 



In a letter on capillarity in Nature for September 

 16, p. 377, Mr. Wilson Taylor shows how difficult it is 

 to account on physical grounds for the phenomena 

 exhibited by liquid films. 



It may not be out of place in the circumstances 

 to refer to Irving Langmuir's views on this subject, 

 given by him in a paper on " The Constitution and 

 Fundamental Properties of Solids and Liquids. II. 

 Liquids" (Am.Chem. Soc, vol. xxxix., September 1917, 

 p. 1852). Langmuir cites a few of the cases in which 

 the forces between the molecules have been considered 

 to be radial forces which vary solely as a function of 

 the distance between molecules. In all these cases 

 the investigator has considered the phenomena to 

 be physical in nature. He then goes on to remark : 

 " The" chemist, on the other hand, in studying the 

 properties of matter, usually employs totally different 

 methods. He is often most interested in the qualita- 



NO. 2764, VOL. I IO] 



tive aspects of the problem, and the quantitative 

 relationships are usually limited to those deducible 

 from the law of multiple combining proportions, the 

 law of mass action, or the principles of thermo- 

 dynamics. When the chemist does consider the 

 forces acting between atoms and molecules, he does 

 not look upon these as forces of attraction between 

 the centres of the molecules, but he thinks rather of 

 the specific nature of the atoms forming the molecules 

 and the manner in which these atoms are already 

 combined with each other. He thinks of molecules 

 as complex structures, the different portions of which 

 can act entirely differently towards any given reagent. 

 Furthermore, he considers that the forces involved 

 in chemical changes have a range of action which is 

 usually much less than the diameter of a molecule, 

 and perhaps even less than that of an atom." 



What has been termed the Classical Theory of 

 surface forces has proved useful in its day ; but it 

 unfortunately ignores chemical affinity. 



R. M. Deeley. 



Tintagil, Kew Gardens Road, Kew, Surrey, 

 September 15. 



Lead and Animal Life. 



Dr. Garrett's communication in Nature of 

 September 16, p. 380, on the effect of a lead salt on 

 Lepidopterous larvae, is particularly interesting to one 

 who has been working on an allied subject. Recent 

 investigations of my own on the fauna of lead-polluted 

 streams in North Cardiganshire, as reported at the 

 Hull meeting of the British Association, point to the 

 presence of dissolved lead - salts in these rivers as 

 distinctly inimical to the aquatic population, in 

 particular to the larvae of certain insect-groups, such 

 as Trichoptera, which are normally non-existent in 

 these streams, though well represented in their 

 neighbours. 



The case of fattening of Weardale sheep on lead- 

 polluted pastures may perhaps provide a parallel ; 

 while it is quite possible that small doses of lead may 

 have a tonic effect, cases of lead-poisoning proper 

 among farm live-stock in general are common in 

 certain districts (see a paper on " Plumbism in N. 

 Cards." by E. Morgan, Journal of U.C.W. Agricultural 

 Dept., 1915), and usually the poisoning is of the type 

 known as " chronic," the effect being slow and cumu- 

 lative, as is also established in the case of lead- 

 poisoning as an industrial disease. It would be 

 interesting to know whether Dr. Garrett's experiments 

 have extended over more than one generation of 

 Lepidoptera, and whether the reproductive faculties 

 were in any way affected. K. Carpenter. 



Department of Zoology, University College 

 of Wales, Aberystwyth. 



Polar and Non-Polar Valency in Organic 

 Compounds. 



There is an increasing tendency on the part of 

 organic chemists to apply the Berzelius dualistic 

 theory, in a modified form, to organic compounds. 

 In many theories of valency, individual groups are 

 considered to be more or less electropositive or 

 electronegative, and it is possible to arrange these 

 groups, approximately, in a table of descending 

 electropositive character. A difficulty which arises 

 in examining this conception is to visualise the 

 transference of anything less than one electron 

 between the group and the remainder of the molecule. 

 There appear to be at least two kinds of forces 

 operating between atoms in a molecule, which can 



