FILARIAL MIGRATIONS TO AND FROM THE CIRCULATION. 243 



I do not anticipate mncli from observations on the disturbing 

 effects of drugs and the febrile state. These undoubtedly in the 

 future will be found to have an influence on filarial periodicity, and 

 it is possible this study may lead to just conclusions as to the cause 

 of the phenomenon. It is not likely, however. The conditions of 

 experiment become in such cases almost too complicated to unravel. 

 We must be careful to bear in mind that substances or forces which 

 interfere with the periodicity may have nothing in common with its 

 normal cause. Assuming that quinine has this power, it would be 

 absurd to infer that the presence or absence in the blood of this drug 

 had anything to do with normal periodicity. It is only by the ex- 

 clusion or inversion of the cause that we may hope to arrive at 

 correct conclusions. 



I have written more than I intended about my speculations on 

 this subject. The great interest you take in these matters is my 

 excuse, and I hope you admit it. 



I will leave speculation alone now, and pass to the facts in ex- 

 planation of the chart I have sent you. 



The chart records a series of observations on the blood, tempera- 

 ture, and pulse of two Chinese lads ascertained to be filarious, and 

 were in the main made by themselves. After enlisting them in the 

 cause, and before commencing systematic observations, I trained 

 them to recognise and count the embryos with the microscope, to 

 read accurately the clinical thermometer, and to record correctly this 

 and observations on the pulse, barometer, and ordinary thermometer. 

 I took care from time to time to satisfy myself that their observa- 

 tions were carefully made and recorded, and I believe if there are 

 any errors in the chart they are few and unimportant. Observations 

 were made every three hours, day and night, during one month. At 

 first the hours selected were^-12, 3, 6, 9, 12, 3, 6, 9 ; but after two 

 days it was found convenient to change them to — 1, 4, 7, 10, 1, 4, 

 7, 10. The quantity of blood was as nearly as possible the same in 

 each examination, just sufficient to form a thin workable film fully 

 occupying a covering glass 1 Jin. by lin. The inevitable differences 

 in the quantities examined probably accounts in part, at least, for 

 discrepancies, in the number of embryos found at corresponding 

 hours on different days. Notwithstanding this unavoidable imper- 

 fection, the microscopical observations serve their purpose, and in 

 the main may be relied on. The same clinical thermometer was 

 used throughout, and by both lads. The instrument I found on 



