June io, 1922] 



NATURE 



747 



of Ochlerotatits detritus, together with a large number 

 of pupae. Titration experiments carried out by Mr. 

 Lyon Turner showed that the salinity of the water 

 was 49 per cent, that of pure sea water. 



After estimating the volume of the water as 

 20,000 gallons, it was decided to use the larvicide in 

 the proportion of i in 16,000, the quantity required 

 being therefore 1-25 gallons. The result of the 

 experiment was entirely satisfactory, a thorough 

 examination on the following day failing to detect a 

 single live larva or pupa. Further examinations 

 were made with the same result on April 26 and May 

 2, and on May 5 the success of the experiment was 

 further confirmed by an examination made by Mr. 

 P. G. Shute (Ministry of Health Laboratory). 



Two other ponds badly infested with the larvae 

 of Ochlerotatus detritus, and containing a large 

 number of pupae, have since been treated with Uke 

 success, a thorough examination of both ponds 

 being made on the following day without a single 

 Hve larva or pupa being found. 



It was noticed during the experiments that the 

 addition of the larvicide to one of the ponds in which 

 the water was only slightly saline, produced the 

 characteristic " milkiness " associated with the use 

 of disinfectants of this class. In treating the other 

 ponds where the water was of greater salinity, this 

 cloudy appearance was not produced, although the 

 results obtained in all the three experiments were 

 equally successful. A series of laboratory tests 

 showed that the " milkiness " occurred whenever 

 the proportion of sea water to fresh water was less 

 than I in 7, the cloudy appearance being uniformly 

 distributed through the water treated. When the 

 larvicide was added to water of greater salinity, it 

 diffused in the form of minute globules. It was 

 suggested by Mr. P. G. Shute that, in cases where the 

 proportion of sea water exceeded one-seventh, the 

 milkiness (and the accompanying uniform diffusion 

 of the larvicide) might possibly still be produced 

 if the larvicide were diluted with a small quantity 

 of fresh water before use. Experiment showed this 

 to be the case, and this preliminary dilution is 

 obviously to be recommended whenever the larvicide 

 in question is to be added to water of appreciable 

 salinity. 



It is probable that successful results will be 

 obtained with even smaller proportions of the larvi- 

 cide than those employed up to the present, since the 

 effects produced with dilution of i in 48,000 indicate 

 that the limit has been by no means reached. Further 

 experiments in this direction are now in progress. 



It is important to note that water treated with this 

 larvicide in the proportions mentioned is quite harm- 

 less to human beings or animals drinking it 

 accidentally. 



The comparative cost of " larviciding " and 

 " paraffining " in any given case depends, of course, 

 upon the depth of water to be treated. In cases 

 where the water is shallow there is little to choose 

 as regards expense, even when the larvicide is used 

 in as large a proportion as i in 16,000. If d be the 

 depth of any particular sheet of water in inches, 

 n the " dilution " (or the number of parts of water 

 which can be treated by one part of the larvicide), 

 and c the ratio of the cost of the larvicide to that 

 of paraffin, then the ratio of the expense of " larvicid- 

 ing " to that of "paraffining" has been shown by 

 Marshall {Science Progress, January 1922, p. 468) 

 to be given by the expression 



(1500 X c X d)/n. 



In the case of the first pond referred to above, d 

 was 3 inches and n was 16,000. The price of the 



NO. 2745, VOL. 109] 



fluid was 5s. gd. a gallon, so that c may be taken 

 as 4. Hence the relative cost of the operation, 

 compared to paraffining, was 



(1500 X 4 X 3)/i6,ooo, or 1-125, 



the actual cost of treating the 1420 square yards of 

 pond being about seven shillings. It should be 

 noted, moreover, that as the water surface in this 

 case was much exposed to wind, paraffining car- 

 ried out on previous occasions had proved quite 

 ineffective. 



Since a cubic yard is the space occupied by 168 

 gallons, it will be found that the number of gallons 

 in any piece of water is (A x<^)i4/3, where A is the 

 surface area in square yards and d is the depth in 

 inches. So that, if the larvicide is to be used in the 

 proportion of i in n, the number of gallons required 

 will be i4/3(Axrf)/w gallons. This is a useful 

 formula for calculation, particularly when a definite 

 value of n has been decided upon for treating a 

 number of ponds. John F. Marshall. 



Seacourt, HayUng Island, Hants. 



The Teaching of Natural History in Schools. 



In an article which appeared in Nature, May 13, 

 p. 628, dealing with the memorandum of a British 

 Association Committee on this subject, the following 

 statement occurred : "It devolves on the teachers 

 of zoology to show in detail the kind of zoological 

 syllabus that can be put into operation in schools 

 as a basis for zoological teaching." May I be allowed, 

 as one whose privilege it has been to teach zoology 

 to some hundreds of boys, to offer one or two sugges- 

 tions for such a syllabus ? 



The writer of the article was entirely favourable to 

 the spirit of the memorandum, as indeed are a great 

 number of persons responsible for the direction of 

 education. With regard to the younger generation, 

 the learners, the question is answered with no un- 

 certain voice. I have put the choice of zoology or 

 botany to forms of boys of all ages from 14 to 18, 

 and have found invariably that 90 per cent, or more 

 vote for the teaching of zoology. It may be that 

 the boys scent my personal leaning towards zoology 

 (though I try to be impartial) or, again, that they 

 regard the study of animals as a more masculine 

 pursuit than the study of plants. At the same time, 

 it is evident that the boy's mind shows a genuine 

 thirst for a knowledge of animal life. 



There are two aspects of the application of zoology 

 to the school curriculum. On one hand, there are 

 the older boys who are being trained for some definite 

 profession — medicine, agriculture, biological research, 

 and so forth. On the other, there are large numbers 

 of younger boys, very few of whom lvitt"ever-4:equire 

 zoology as a professional subject, who are being taught 

 biology as part of their general education. Zoological 

 syllabuses for the professional examinations are 

 issued by the various universities ; moreover, in the 

 Higher Certificate Examination zoology may be 

 offered as a group subject. Thus, in the case of 

 senior boys the biology master has ample guidance 

 in the general requirements of a zoological education, 

 and can develop and extend his teaching accordingly ; 

 but in teaching zoology to younger boys the master 

 has to evolve his own syllabus and to form his own 

 standard of attainment. It is with the latter aspect 

 of the subject that I propose to deal. 



The boy of fourteen when he comes to the study 

 of biology requires something more substantial than 



