362 Mr. Plimmer and Capt. Fry. Further Results of [June 28, 



to show that some portion of the metal introduced must be changed into 

 some soluble form very rapidly ; but apparently after the reaction of the 

 tissues occurs the antimony becomes more or less shut off, and absorption 

 must take place very slowly, as traces of the metal, apparently unaltered, 

 have been found as late as six to seven weeks after the injection. 



Sodium antimony lactate and antimony sodium calcium lactate were 

 found to act rather more slowly than the above (see Table above), the time at 

 which the trypanosomes had completely disappeared varying from three to 

 four hours. 



It was noticed in these experiments that trypanosomes, though obviously 

 drug-affected when the blood was taken, remained alive on the slide outside 

 the body for a long time after all forms had disappeared from the circulating- 

 blood. 



Further details of the time taken for the various drugs to act will be 

 found in the sections upon sodium antimony lactate, antimony oil, antimony 

 egg-yolk, and arsenophenylglycin. 



On the Action of Trypanocidal Substances in vitro. 



Experiments have been carried out with a view of throwing light on the 

 more exact nature of the changes which are produced in trypanosomes when 

 they are brought into contact with trypanocidal substances. The general 

 principles we have observed in these experiments have been : 1. To dissolve 

 the drug in some fluid so that when it is added to the infected blood it will not 

 cause osmosis to occur in the cellular elements of, or trypanosomes contained 

 in the blood. (The various substances were dissolved in a 0'89 per cent, salt 

 solution, isotonic with rat's blood which was used in these experiments.) 



2. To use always equal volumes of the solution and of the affected blood. 



3. To use blood at the time when the trypanosomes are just becoming very 

 numerous, so as to avoid the presence of old, feebly moving forms, which are 

 always present in the later stages of an acute infection. The method of 

 observation has been to watch the behaviour of the trypanosomes when in 

 contact with the . various solutions of the drug under the microscope. 

 A measured drop of blood and of the solution are mixed on a slide with 

 care : the mixed drop is then covered with a sufficiently large cover glass, 

 and this is sealed with vaseline. 



It has been found possible in this manner to exactly determine the 

 dilutions at which the various drugs used cease to have an instantaneously 

 trypanocidal action ; further, in higher dilutions, by carefully watching the- 

 changes taking place in the trypanosomes, it is possible to determine the 

 dilution at which no effect is produced, and between these two points- 



