APPENDIX II 417 



of living and dead cells in them. The agar jelly can be made from 

 stock solutions as specified and kept in test-tubes for months, as 

 moulds will not grow on it. Films are rapidly prepared by boiling 

 the jelly in a tube in a spirit-lamp flame. 



With regard to the two disadvantages, an incubator working 

 at 30 C. is not usually within reach even in laboratories, although 

 Hearson's apparatus will maintain this temperature if fitted with 

 a special capsule. Since my aim is to make this possible diagnos- 

 tic method suitable for practical purposes even away from the vicin- 

 ity of a laboratory, I dispense with an incubator and employ the 

 ordinary temperature of a room, say between 60 and 70 F. In 

 order to do this the citrate solution is modified. If the solution 

 already specified were used at such a temperature the leucocytes 

 might live for a long time even in an infected plasma, and a day 

 or two might elapse before sufficient deaths occurred among the 

 cells to make a contrast. Consequently I deliberately shorten the 

 life of the cells by using a solution containing 1 . 2-per-cent sodium 

 citrate and 1-per-cent sodium chloride. As the same solution is 

 employed for all tubes the artificial shortening of life does not 

 appear to vitiate the results. There are several ways by which 

 this shortening of life can be accomplished, though I consider the 

 lowering of the sodium citrate content to be the most suitable. 

 Using this solution it has been found that the majority of healthy 

 cells in another healthy person's plasma are dead in about 24 hours 

 if kept at the room temperature, which, of course, may be variable. 

 So a contrast can usually be obtained within 24 hours of mixing 

 the bloods. With regard to the second disadvantage, I hope by 

 experiment to ascertain the minimum number of leucocytes which 

 it may be necessary to count to obtain a trustworthy average. I 

 am sure that a smaller number than 500 will be sufficient. I am 

 also experimenting with a greater concentration of plasma with a 

 view to obtaining a wider contrast between the length of the 

 lives of cells in healthy and infected plasma. 



In conclusion, I wish to suggest that this method may also be 

 useful from a medico-legal aspect, for I have found the leucocytes 

 alive in the blood removed from the hearts of bodies which have 

 been lying in the mortuary for 24 hours or more, and it may be 



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