100 Dr.J.O.WakelinBarratt. Lethal Concentration [June 15, 



"The Lethal Concentration of Acids and Bases in respect oi 

 Paramcedum aurelw." By J. 0. WAKELIN BARRATT, M.D., 

 B Sc f , Lond., British Medical Association Eesearch Student. 

 Communicated by Sir VICTOR HORSLEY, F.K.S. Keceived 

 June 15, Read June 16, 1904. 



(From the Physiologisches Institut, Q-ottingen.) 



The present investigation arose out of a research on chemiotaxis, in 

 the course of which it became apparent that a pre-condition of the 

 correct understanding of the nature of chemiotaxis is the quantitative 

 determination of (1) the concentration of the acid and alkaline solutions 

 employed for the study of chemiotactic phenomena, and also of (2) the 

 absolute weight of Paramoacia (or other organisms) added to such 

 solutions. So long as these data are unknown, chemiotaxis can only 

 be investigated qualitatively, and such facts as are ascertainable solely 

 by means of quantitative observations lie beyond the limits of research. 



In order that the acid and alkaline liquids employed may be readily 

 comparable one with another, equimolecular solutions are employed in 

 this investigation. The absolute volume of Paramoecia employed in 

 the different experiments was determined by means of the hsemocrit, 

 as in the case of red blood-cells, and from this the weight of Paramoacia 

 was ascertained. In those experiments in which an approximate 

 determination of the weight was sufficient, the Paramcecia were counted, 

 a modification of the method used for the enumeration of red blood- 

 cells being adopted. 



In all cases the Paramcecia were obtained in as nearly as possible 

 the same condition. They were removed by centrifugalisation from 

 the liquid in which they had been cultivated, and placed in a large 

 bulk of distilled water for 24 hours before use. At the end of this 

 time they were again concentrated, by centrifugalisation, into a small 

 bulk of fresh distilled water, and were ready for use. In this way 

 contamination of the acid and alkaline solutions employed was avoided, 

 and the modification of chemiotactic reaction brought about by the 

 medium used for cultivation was also, as far as possible, avoided. " 



The method of investigation adopted for determining the lethal 



concentration of acids and alkalies consisted in placing Paramoecia in 



solutions of gradually decreasing molecular concentration, arranged so 



as to form a geometrical series, each succeeding concentration being 



that of the preceding, and noting the time at which death occurred. 



i all the experiments quoted, in order to make certain that the 



xtremely dilute solutions employed were accurately prepared, their 



relative conductivity was determined. The latter was measured by 



deflection of a sensitive galvanometer, when a fixed potential 



