288 Mr. E. Ponder. A Method for Investigating the 



control respectively. This method of deciding the end-point is very satisfac- 

 tory, as, if the tube be inspected by transmitted light alone, without a dark 

 background, the time taken for complete hcemolysis will be much under- 

 estimated. The moment when complete haemolysis occurs is noted ; the time 

 taken for the particular dilution of hsemolytic agent to haemolyse 1 c.c. of 

 standard blood suspension at the particular temperature employed is then 

 known. 



If the time for haemolysis is long, the contents of the tubes should be 

 stirred with the thermometer each half-hour. 



If 4 c.c. of the dilution of haemolytic agent contain 5 mgrm. (that is, a 

 1-10 dilution of the original solution prepared), then, when 1 c.c. of the blood 

 suspension is added, the 5 c.c. in the tube will contain 5 mgrm. of hsemolytic 

 agent, or a I'lOOO dilution (ignoring the negligible volume of the erythrocytes). 

 In this way the dilution employed for producing haemolysis is kept in round 

 figures and readily calculable. 



This method of investigating haemolytic activity has been applied to a 

 number of htemolytic substances. Those investigated were the following : — 



Saponin. Acetic acid. 



Sodium taurocholate. Citric acid. 



Sodium glycocholate. Benzoic acid. 



Lactic acid. Ammonium chloride. 



It has been found possible to describe the action of these substances by formulae. 



It is to be remembered that, while the general forms of these formulas are 

 correct for the action of these substances on blood suspensions of any concen- 

 tration, the values of the various constants in the equations will vary for 

 blood suspensions of different concentrations, and even for suspensions of the 

 same concentration, of blood cells derived from different individuals or 

 animals. 



Relation between Time and Teniperatiire. 



In the cases of all haemolytic substances examined, it has been found by 

 experiment that there is a definite relation between the time taken for a 

 given quantity of the substance to produce complete haemolysis of 1 c.c. of 

 standard blood suspension, and the temperature at which 'the experiment is 

 conducted. As the temperature is increased, the time taken to produce 

 complete htemolysis becomes less. 



If T = the time, in minutes, taken to produce haemolysis of 1 c.c. standard 

 blood suspension, 



and T = the temperature at which the experiment is conducted, in degrees 

 centigi'ade. 



