128 MORPHOLOGIC VARIATION 



in actual number of living cells, the microscopic counts which indi- 

 cate not only the death of the cells but also their complete autolysis 

 and disappearance, and the proportion of cells stained by Congo 

 red. These values are given in Table XXVI. The property of 

 staining by Congo red, as was described in Chapter III, indicates 

 not only the death of the cells but also that they have undergone 

 a certain degree of autolysis. This being the case, as death proceeds 

 the plate counts should show a marked decrease before the micro- 

 scopic counts, and the proportion of stained cells should also increase 

 at a slower rate than the plate counts decrease. Such was found 

 to be the case. In order to show these three quantities graphically, 

 in a form in which they might be directly comparable, the curves 

 have been plotted in the following manner: The percentage of de- 

 crease from the maximum plate count was computed for the first 

 day in which a decrease was noted, and to this was added day by 

 day the further decreases in number of cells as a percentage of 

 the maximum number attained in the culture. Thus we obtain a 

 cumulative percentile curve which is directly comparable to the 

 curve for the percentage of stainable cells, which of course is also 

 cumulative. In a similar manner a curve for cumulative percentile 

 decrease in the number of cells in microscopic counts was plotted. 

 These three curves are given side by side for each of the five cul- 

 tures in Figure 36. It will be seen that in every case the curve 

 for percentage increase in stained cells (dotted line) occupies a 

 position between the curve for percentage decrease in viable cells 

 (solid line) and the percentage decrease in microscopic counts (dot 

 and dash line). 



In most cases the decrease in microscopic counts was not marked 

 even at the end of twenty-five days. Their curves are therefore 

 not completed and not easily compared with the curves for plate 

 counts. The curves for stainable cells, however, are nearly complete 

 in most cases, and the distance between these curves and the curves 

 for plate counts then serves as a fairly good measure of the rate 

 of autolysis in the culture. This measure can be best taken on 

 the 50 percentile line, and is indicated in the graph, the figures 

 given being the number of days which have elapsed from the time 

 that half of the cells were dead, as determined by the plate counts. 



