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NATURE 



[January 17, 19 il 



criminal intent. The term "food poisoning " is 

 here limited to the occasional cases of poisoning 

 from organic poisons present in normal animal or 

 plant tissues, the more or less injurious conse- 

 quences following the consumption of food into 

 which formed mineral or organic poisons have 

 been introduced by accident or with intent to im- 

 prove appearances or keeping quality, the cases of 

 infection due to the swallowing of bacteria and 

 other parasites which infest or contaminate certain 

 foods, and the poisoning due to deleterious sub- 

 stances produced in food by the growth of bac- 

 teria, moulds, and similar organisms. We have no 

 certain statistics of the frequency of food poison- 

 ing, but Mr. Jordan has collected data of more 

 than 1000 cases occurring in the United States in 

 the two years October, 1913, to October, 191 5. 



In the chapter dealing with poisonous plants 

 the poisonous fungi claim most attention. Some 

 reference might have been made to the nutmeg, 

 which is distinctly toxic in large doses, and in 

 smaller doses to some individuals. In the section 

 dealing with food-borne, disease-pfoducing bac- 

 teria, the sub-heading is "Paratyphoid Infection," 

 and this term is used many times. What is really 

 meant is Gartner (B, enteritidis) infection, and this 

 organism is distinct from the paratyphoid bacilli, 

 though belonging to the same group. Ptomaine 

 poisoning is too briefly referred to, and we note 

 the omission of all allusion to tyrotoxicon, which 

 is somewhat surprising. One of the best sections 

 is that dealing with food preservatives, to which 

 several pages are devoted. In conclusion, refer- 

 ence is made to such conditions as beri-beri, 

 pellagra, lathyrism, scurvy, etc. The book is 

 well produced, very readable, and illustrated with 

 several figures. ' R. T. H. 



Adolescence. By Stephen Paget. Pp. 59. (Lon- 

 don : Constable and Co., Ltd., 1917.) Price 

 yd. net. 

 L\ the adolescent mind ideas of sex and religious 

 Ideas often grow up together, and they should 

 be correlated. While there is a wide range of 

 individual peculiarity within the limits of the 

 normal, there is no virtue in a child's being in- 

 curious. Careful preparation should be made by 

 parents and teachers so as to give well-considered 

 and honest answers to embarrassing questions. 

 Perhaps there should be a home-ceremony or 

 an initiation, " the whole thing well thought out, 

 the exhortation written down beforehand, every 

 word of it. " " First-rate school teachers are more 

 likely than second-rate parents to say the right 

 thing to children." "The reasonable soul and 

 flesh is one man," and there must be disciplining 

 of both sides. " If I could be a young man again, 

 I would get on without alcohol and cigarettes. . . . 

 Let me, as a doctor, add a good tonic to steady the 

 nerves of adolescence. I prescribe a full dose of 

 the natural sciences." " What does harm the 

 minds of children is not our plain speaking ; it is 

 their own secret reading, gossiping, and imagin- 

 ing. " "And — so far as adolescence is concerned 

 — If ever there was a time when w^e ought to speak 

 .plainly, It Is now." 



NO. 2516, VOL. 100] 



i LETTERS TO THE EDITOR. 



I [The Edilur does not hold himself responsible for 

 I opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 j the writers of, rejected manuscripts intended for 

 I this or any other part of Nature. No notice is 

 I taken of anonymous communications.] 

 Sources of Potash. 

 Sir Eoward Thorpk's lucid review of the knowa 

 geological sources of potash (Nature, January 3) is of 

 absorbing interest to agriculturists, whose industry 

 must be seriously affected by any permanent stinting in 

 the supply of this indispensable fertiliser, entailing a 

 corresponding diminution in the production of root 

 crops. They might, however, tide over a temporary 

 shortage of potash by availing themselves of a subsidiary 

 source. 



The Boards of Agriculture for England and Scotland 

 having recently issued leaflets directing attention to the 

 high percentage of potash contained in bracken fern.. 

 Prof. H. G. Greenish, director of the Pharmacy Re- 

 search Laboratory in IBloomsbury Square, very kindly 

 undertook at my request to make analysis of the ash 

 of incinerated bracken. As it had been stated that the 

 amount of potash contained in the fern cut in autumn 

 showed a considerable diminution compared with that 

 cut at midsummer, I sent Prof. Greenish three con- 

 signments, cut respectively in July, September, and, 

 after the plant had withered, in November. The result 

 proved practically the same in each case, and I may 

 quote as follows from Prof. Greenish 's very full re- 

 port : — 



" I find that the fern, when dried in a warm room and 

 completely burnt to a nearly white ash, yields 4-82 per 

 cent, of ash. This ash contains 41-5 per cent, of potash, 

 K„0. The dried fern itself would therefore yield 

 2 per cent, of potash, or 50 tons of fern would yieW 

 about 2-41 tons of ash, in which there would be' about 

 one ton of potash. ... In addition to the potash the 

 ash contains small quantities of soda, phosphates, 

 sulphates, and chlorides." 



It is clear from this that, although bracken can 

 never compete with geological deposits as a source of 

 potash, a considerable amount might be recovered by 

 harvesting and burning the fern under a proper system. 

 At the same time, it would tend to rid the land of a 

 pest which has destroyed much of the best hill pasture 

 in the North, and is spreading year by year. 

 Bracken will grow only on good land ; it cannot thrive 

 on marsh. The destruction of pasture is far from 

 being the only evil ; animals feeding among bracken 

 get their heads and necks covered with ticks — in fact, 

 the death of a considerable number of sheep in this 

 countv seems to be justly attributed to this cause alone. 

 If, therefore, land can be cleared of a most pernicious 

 weed, and, at the same time, a valuable manure ob- 

 tained for tillage, there are niany farms where the work 

 might be profitably undertaken. 



The analogy of kelp presents itself. I understand that 

 it takes from twenty to twentv-two tons of good wet 

 seaweed to produce a ton of kelp, which yields between 

 30 and 40 per cent, of potassium salts, more than 

 double the return from an equal weight of dried fern,, 

 besides the iodine which is recovered from kelp. But, 

 on the other hand, it is far easier to cut bracken than 

 to gather deep-sea tangle, and the ash can be used as a 

 fertiliser on the farm where it is burnt. 



Driving lately from Dorchester to Abbotsbury, I saw 

 hundreds of acres of downland rendered alssolutely 

 valueless bv bracken, whereof the luxuriant growth 

 betokened a soil well adapted either for tillage or 

 forestry. Herbert Maxwell! 



Monreith, Whauphill, Wigtownshire, N.B. 



