3l8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



small, in consequence consuming less of the food provided 

 for them by the leguminous plant. Starch can therefore 

 accumulate in the uninfected cells from which the infected 

 cells are osmotically supplied with food. Depositing the 

 non-nitrogenous food in solid form (starch) of course re- 

 duces the turgor pressure in the cells of the tubercle and 

 thereby reduces the resistance to the plaster investment. 

 The component cells of the tubercle enclosed in plaster of 

 Paris remain smaller than in unconfined tubercles, the in- 

 fected and uninfected cells being more nearly equal in size. 



Enclosing a tubercle in plaster may diminish the stimulus 

 or inflammation produced in the cells by the bacteria, but 

 as the bacteria survive and multiply there can be no great 

 diminution of their chemical effect on the cells in which 

 they occur. The physical result, pressure, is much more 

 affected by the plaster investment. Since the infected cells 

 remain more nearly the same in size as the uninfected ones, 

 the inference is plain that the excessive increase in size of 

 the infected cells is due to increased pressure in them. 



The infected cells, as shown by figure 8, are thin-walled 

 and contain only one large vacuole. This is not traversed 

 by cytoplasmic strands. The quantity of bacteria may vary 

 in infected cells, and with this there is a corresponding vari- 

 ation in the appearance of the cells. Thus, fig. 8 shows a 

 typical infected cell in which the bacteria have multiplied 

 enormously, while fig. 9, magnified about one-third larger, 

 represents a cell in which there are comparatively few bac- 

 teria, most of which are at the point indicated by the line 

 from B. In the cells containing relatively few bacteria 

 there may be some starch-grains, as indicated by the line 

 from S. In unstained hand-sections, the degree to which 

 the older parenchymatous cells in the central part of a 

 tubercle are infected is indicated at a glance by the amount 

 of starch in the cells, the cells with the average amount of 

 bacteria containing no starch-grains, the cells with no bac- 

 teria containing many starch-grains, the cells with few 

 bacteria containing starch grains in inverse proportion to 



