1922] McDonald: On Baknitidiuni coli and Balantidiinn suis 257 



with the same fluid (in separate contaiiiei-s) and in the same water 

 bath. Thence to 70 per cent alcoliol the treatment continued identical. 

 One hundred individuals from each sample of material were measured. 



From these measurements the graplis shown in figure B were con- 

 structed in the same manner as the previous one, except that the 

 curves of the separate samples were plotted separately on the same 

 axis. The continuous line represents the individuals from one pig and 

 the broken line those from the other. The mode of the first curve 

 occurs at 1.3. If the ratios 1.2 and 1.4 be included with 1.3, it is found 

 that 80 per cent came within these limits. Of the entire number of 

 individuals in the lot only one showed a ratio of 1.6 and one as high 

 as 1.7, while there were none with a higher ratio. The second curve 

 reaches its highest point at 2.0, while 71 per cent of the entire number 

 measured is included between 1.8 and 2.2. A number of individuals 

 have ratios above 2.2, while one had a ratio as great as 2.7. Five indi- 

 viduals have ratios below 1.6, at which point the curves begin to over- 

 lap ; but in practically every one of these individuals there were 

 observed characters (which are discussed below) that made it quite 

 evident that they were really of the type represented by the other 

 curve. 



Upon comparing figures A and B their likeness is very striking, 

 the second being corroborative of the results shovra by the first. That 

 both are bimodal is evident. However, the low points, the point of 

 demarcation of the two groups, do not occur at the same place; 

 in the first it is at 1.4, while in the second it occurs at 1.6. Also the 

 median of the first mode in figure A occurs at 1.2 while in figure B 

 it is at 1.3, and the median of the second mode in figure A is at 1.7 

 while in figure B it occurs at 2.0 ; that is, in figure A the entire curve 

 is shifted to the left, meaning that all ratios are decreased or that all 

 individuals approach nearer to the spherical shape. This shifting is 

 greatest in the case of the second mode. This in conjunction with 

 the greatest breadth of the second curve in figure B is what would 

 be expected if the premise in regard to the effect of fixation discussed 

 above (page 251) is correct. Extra care was used in the fixation of 

 tlie latter lot of material whereas in the former only the ordinary pre- 

 cautions were taken. At any rate these differences between the two 

 groups do not detract from the evidence which they offer that there 

 are two distinct types of balantidia parasitic in pigs. 



The value of these curves in showing race or species differentiation 

 is directly proportional to the extent to which any other factors which 



