September 15, 1923] 



NA TURE 



\97 



which inaccuracies in the potassium iodide method 

 of estimation, namely, the interference of sulphur 

 dioxide and serious loss of iodine by volatilisation, 

 were overcome by first removing the former, and 

 then allowing the ozonised air to react on potassium 

 iodide in the presence of a known volume of N/ioo 

 thiosulphate solution, which fixes the liberated iodine. 

 The apparatus used will be described later, together 

 with the general results. 



The measurements form two series, determinations 

 of the sulphur dioxide and nitrogen peroxide in 

 dilute sodium bicarbonate, alternating with those of 

 ozone, sulphur dioxide, and ammonia. Each test 

 proceeds for about three days, and is conducted in 

 duplicate at the village of Upminster, Essex (17 

 miles E.N.E. of Charing Cross), and at Messrs. Jeyes' 

 laboratory, Plaistow, E., 5000-10,000 litres of the 

 outside air in each case being examined. The former 

 estimation was in progress during the storm at both 

 places. Upminster lay on the eastern fringe of the 

 storm track. It experienced severe lightning, but 

 only o"36 inches of rain fell there, as against 2 inches 

 at the London station, which was nearer the centre. 

 The proportion of nitrogen peroxide before, during, 

 and after the storm (recorded in terms of i volume 

 of XO, in . . . million volumes of air) was as follows : — 



There was, therefore, no appreciable increase in 

 nitrogen peroxide in the air during the storm. The 

 sulphur dioxide and ammonia remained practically 

 constant during the above period, the proportion of 

 the former being — London, i in 20 millions, Up- 

 minster, I in 45 millions, while the ammonia amounted 

 to I in 200 millions in both. 



This result has been confirmed by an examination 

 of rain water. I have not yet collected during a 

 thunderstorm a specimen of London rain sufficiently 

 free from suspended particles (which completely 

 mask its analysis) to be trustworthy ; but in a bright 

 sample collected during a thunderstorm at Up- 

 minster, the nitric acid content proved to be equiva- 

 lent to a N/200,000 nitric acid solution, which is 

 slightly under the average of several samples collected 

 during still conditions. 



The proportion of ozone present a few days before 

 tlie storm was i in 23 millions in London, and i in 

 22 millions at Upminster, but the average amount 

 present between July 13 and 16 was i in 3-2 millions 

 in London, and i in 14-8 millions in the country. 

 1 here was, therefore, more than seven times the previous 

 quantity of ozone present in London air three to six 

 days after the storm, and the proportion must have 

 ■ ''cn appreciably higher than this at the time, owing 

 the subsequent loss by diffusion and convection, 

 ,.;id to the change into oxygen, which can be readily 

 proved to occur. A fortnight later the proportion 

 of ozone at both places was i in 18-5 millions. 



Confirmation of the above results has been obtained 

 I luring a much less spectacular thunderstorm, which 



ited both stations about midday on August 24 



t. A few days previously the proportion of 

 o/.one found was — London, i in 22-7 millions, Up- 

 minster, I in i8'8 millions. Measurements of the 

 o/one had been in progress nearly twenty-four hours 

 u hen the storm occurred, and were continued for the 



\t three days. The average content for the four 



vs was — London, i in 9.71 millions, Upminster, i 

 ni 7-8 millions, the proportion of ozone having thus 

 been more than doubled in each instance. 



I hope to devise a portable modification of the 

 apparatus that v/ill enable estimations to be com- 

 pleted in two or three hours, in which case much more 



NO. 281 I, VOL. 112] 



detailed information on the subject will be obtained 

 than is possible in three- to four-day averages. 



William C. Reynolds. 

 " Wharf edale," Upminster, Essex, 

 August 28. 



A Method for Demonstrating the Stages in the Life 

 History of Monocystis in Practical Class Work. 



In the text-books on practical zoology in common 

 use in zoological laboratories, the method advocated 

 for making preparations of the contents of the 

 vesiculae seminales of the earthworm for the examina- 

 tion of the stages in the life history of Monocystis is 

 what is usually known as the cover-glass method 

 [vide Marshall and Hurst, " Practical Zoology," 9th 

 edition, p. 13). It is, I believe, a matter of common 

 experience that, when this method is adopted, only a 

 small percentage of the students succeed in finding 

 in their own preparations all, or even the majority, 

 of the important stages. Generally only the tropho- 

 zoite and sporocyst stages are found, and demonstra- 

 tion specimens have to be resorted to to fill in the gaps. 



This repeated failure in previous years suggested 

 the trial of a modification of the method, and the 

 result may be of interest to those who have charge of 

 practical classes. The preliminaries are the same. 

 The vesiculae seminales (preferably the posterior 

 lateral vesiculae seminales, as these appear to contain 

 more specimens) are removed from a freshly killed 

 (with chloroform) worm, and placed in a watch-glass 

 with about five to six times their bulk of normal salt 

 solution. The material is teased thoroughly with 

 needles. A drop of the fluid and particularly a 

 portion of the teased wall of the vesicula seminalis is 

 placed on a slide and, if desired, faintly stained with 

 Dahlia. Cover with a cover-glass, and the preparation 

 is ready for examination. If the operation has been 

 rapid and the staining only slight, the trophozoites 

 will be found to be still alive and exhibiting the 

 characteristic gregarine movement. The encysted 

 stages will be found embedded in the tissue of the wall 

 of the vesicula seminalis, and it is for this reason that 

 stress should be laid upon the inclusion of a portion 

 of the wall in the preparation. In this situation the 

 stages which are not usually found, i.e. the gameto- 

 cytes in association, and more rarely gametocytes 

 showing fragmentation into gametes, occur, as well 

 as large numbers of sporocysts containing spores. 



Below is a summary of the results (as recorded by 

 the students themselves) obtained with a class of 

 twenty students, one worm serving for every two 

 students. The class was held in May. 



cf„,„„ Percentage of students 



'''»'^^- obtaining Stages. 



Trophozoite 85 



Gametocytes in association . . 60 

 Gametocytes showing fragmentation 



into gametes 25 



Sporocysts with spores • • • 95 

 As experience shows, worms vary considerably in 

 the extent to which they are infested with Monocystis, 

 but the above result may be taken as representative. 

 It may be of interest also to record that the worms 

 used by the class had been kept in the laboratory from 

 the previous November. The method adopted was 

 to keep them in a tank in a compost made up of one 

 third earth and two-thirds moist leaf-mould. The 

 compost must be kept reasonably moist, and it was 

 found advantageous to change it about every three 

 weeks. A. J. Grove. 



Zoological Laboratory, 

 The University, Sheffield, 

 August 21. 



