496 



NATURE 



[September 14, 1905 



The smallest measurements ever jet made, viz. 

 1/2,000,000 millimetre, were in connection with the move- 

 ments of a telephone diaphragm. The problem was to 

 find what movement of the diaphragm produces a sound 

 which is only just audible. 



This is done as follows : — Place a telephone to the ear 

 and pass through it a steady current. On stopping the 

 current a sharp sound is heard in the telephone. Alter the 

 strength of the current until when it is stopped the sound 

 can only just be heard. Observe on a galvanometer the 

 strength of that current (c). Next put the telephone in 

 the electric micrometer in place of the rod R, pass the 

 current (c), and measure the movement of the diaphragm 

 in the usual way. This movement then produces a sound 

 in the telephone which is just audible. 



Another use of the instrument is to measure the sparking 

 distance between two surfaces, the potential difference of 

 which is known. The surfaces used are p, o in the figure. 

 Suppose the potential difference between these surfaces is 

 very small, say i/iooo volt. Find the contact position 

 as above, and draw p away from o. Now make the 

 potential difference between p and Q equal to i volt. On 

 making p approach o the contact position has changed 

 by an amount D. Thus the sparking distance for i volt 

 is D (supposing the spark distance for i/iooo volt is 

 negligible). This is found to be about 1/100,000 mm. 



In problems on the constitution and molecular pro- 



aiTTS" 





perties of matter there are obvious possibilities before this 

 apparatus, for by it we can bring two surfaces of any 

 hard metal to molecular distance (or less) from one another, 

 and keep them there while any desired physical change is 

 produced in the surfaces or in the medium surrounding 

 them. 



THE BRITISH ASSOCIA TION. 

 SECTION I. 



PHYSIOLOGY. 



Opening Address by Colonel D. Bruce, M.B., F.R.S., 

 C.B., President of the Section. 



The Advance in our Knowledge of the Causation and 

 Methods of Prevention of Stock Diseases in South Africa 

 during the last ten years. 



Ten years ago, when I first came to South .'\frica, I 

 was led to take an interest in the various great stock 

 diseases which do so much damage and so retard the 

 progress of South Africa as a stock-raising country. I 

 thought, therefore, that a good subject for my address, in 

 the centre of the foremost stock-raising Colony of South 

 Africa, would be a review of the work done in advancing 

 our knowledge, during the last ten years, of the causation 

 and methods of prevention of stock diseases in South 

 Africa. South Africa is particularly rich in animal 

 diseases, every species of domestic animal seemingly having 

 one or more specially adapted for its destruction. Now 



NO. 1872, VOL. 72] 



it is evident that, in an address of this kind, it will be 

 impossible to take up every stock disease, but I think you 

 will agree with me that those shown on this table are 

 among the most important : — 



East Coast Fever ; ordinary Redwater or Texas Fever ; 

 Biliary Fever of Horses ; Malignant Jaundice of Dogs ; 

 Nagana or Tsetse-fly Disease; Trypanosomiasis of Cattle r 

 Rinderpest ; Horse-sickness ; Catarrhal Fever in Sheep ; 

 Heart-water of Sheep, Goats, and Cattle. 



No%v we may group these diseases in various ways ; for 

 example, as below, where they are divided into two main 

 divisions : .4 division, in which the parasite is known : 

 and B division, in which the parasite is unknown. 



.•1. Parasite known. 



I. Diseases caused by parasites belonging to the genus 

 Piroplasma : — 



(i) East Coast Fever (Koch), P. farvum. 



(2) Redwater or Texas Fever, P. bigeminuin (Theiler). 



(3) Biliary Fever of Horses, Mules, and Donkevs, 

 P. equi. 



(4) Malignant Jaundice of Dogs, P. canis. 



II. Diseases caused by parasites belonging to the genus 

 Trypanosoma : — 



(i) Nagana or Tsetse-fly Disease, T. brucci (Bradford 

 and Plimmer). 



(2) Trypanosomiasis of Cattle, T. theilcri (Bruce). 



B. Parasite unknown. 



I. Rinderpest. 



II. Horse-sickness. 

 Catarrhal Fever of Sheep. 

 Heart-water of Sheep, Goats and Cattle. 



I. Diseases caused by Par.asites belonging to the Genus 

 Piroplasma. 

 (i) East Coast Fever. 

 The first important stock disease I would direct your 

 attention to, then, is East Coast Fever. This name was 

 given to it by Prof. 

 Robert Koch, of Berlin. 

 In the Transvaal the 

 disease is usually called 

 Rhodesian Redwater. 

 This term is not a 

 good one, since the 

 disease is not restricted 

 to Rhodesia, nor did it 

 arise there, nor is this 

 a disease similar to the 

 ordinary Redwater. 



Ten years ago. East Coast Fever was unknown in the 

 Transvaal. The first known outbreak occurred only 

 some three and a half years ago, when it broke 

 out at Koomati and Neilspruit, in the Barberton dis- 

 trict, and in the east of the Colony. The disease 

 had broken out some time previously in Rhodesia, and 

 the outbreaks in both Colonies were due to infection 

 from Portuguese territory. Although this disease has only 

 been introduced to the country during the last few years, 

 it has already produced an enormous amount of damage 

 among stock, and is probablv the most dangerous disease 

 that the people of the Transvaal have to cope with at the 

 present time, and for some years to come. 



In the Annual Report of the Transvaal Department of 

 .'Vgriculture there is a most excellent report by Mr. Stock- 

 man, the then Principal Veterinary Surgeon, on the work 

 of the veterinary division for the year 1903—1904. A large 

 part of this report is given up to East Coast Fever, and 

 I must here express mv indebtedness to Mr. Stockman 

 for much of the follow'ing account of this disease. In the 

 same Annual Report there is also an account by Dr. 

 Theiler, the Veterinary Bacteriologist, of the experimental 

 work. Messrs. Stockman and Theiler evidently worked 

 together, and I must congratulate them on the immense 

 amount of good, useful work done by them, and I would 

 also congratulate the Government on having had the 

 services of two such accomplished and energetic gentlemen 

 during the late troublesome times. Unfortunately for the 

 Transvaal, Mr. Stockman has accepted the post of 

 Veterinary Adviser to the Board of Agriculture in England, 



