412 APPENDIX II 



two that the result can be determined. In other words, all 

 measurements must be simultaneously controlled by other measure- 

 ments and the contrast is the result. It is also obvious that since 

 heat and the citrate solution both affect the lives of the cells, all 

 tubes, whether containing infected or control plasma, must be 

 subjected to the same conditions as regards temperature. And it 

 is essential that the same citrate solution must be employed both 

 for the test and the control. Unless these essential details are 

 adhered to, any measurements may be considered to be worthless. 

 Leucocytes are very sensitive to changes in temperature when they 

 are resting in citrate solution, but if a change occurs and all tubes 

 are subjected to 'the same change the contrast in the length of life 

 holds good. The most favourable arrangement of the citrate 

 solution has already been given. It should be quite neutral, 

 because if alkaline it shortens the lives of the cells. 



Leucocytes appear to live longest at about 20 C. They will 

 not live very long at 37, and at 10 will live longer than at 37 but 

 not so long as at 20 C. I have already suggested (4) that this 

 may be due to the accelerated absorption of the poisonous salts in 

 the citrate solution caused by heat, and this will also explain the 

 early death in the presence of alkali which also accelerates diffusion. 

 I presume that the reason why they live longer at 20 than at 10 

 is because their normal temperature is about 37 C. and that they 

 die in the cold in spite of the delayed absorption. 



In the following experiments a temperature of 30 C. was em- 

 ployed with the specified citrate solution, and control experiments 

 were conducted in each case, the results given being the difference 

 in the measurements between the test and control. 



Measurements 



Length of the life of healthy person's leucocytes when resting in 

 their own plasma^ As has been shown in a former paper (2), an 

 average shows that all the cells are alive in 24 hours; the majority 

 are alive in 36 hours; about 50 per cent are dead in 48 hours; 

 and all are dead in 86 hours. 



. Healthy person's leucocytes; other healthy person's plasma. All 

 cells were alive in 14 hours; about 50 per cent were dead in 18 



