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



Flemming's strong mixture (i) proved decidedly the 

 best in most cases ; very fair results were obtained also 

 with iridium chloride (8), platinum chloride (16), palla- 

 dium chloride (11), and Flemming's strong mixture with an 

 excess of chromic (4). Reiser's sublimate-acetic (39) 

 gave good results in some cases. 



Some objects could not be satisfactorily fixed in any of 

 these. In such cases good results were usually obtained 

 by the use of Flemming's strong mixture with the acetic 

 omitted (5); where this failed resort was had to fixing in 

 potassium iodide-iodine (22) and transferring after a longer 

 or shorter time to Flemming's strong mixture. 



In most cases fixatives were found which produced no 

 visible change in the structure of the living cell so far as 

 could be ascertained by careful observation with high 

 powers during the application of the fixative. It was 

 found, however, that material placed in some of these fixa- 

 tives undergoes structural alterations after a few hours ; in 

 these cases the time of fixation was shortened accordingl}^ 



During the formation of the spindle the cell is more 

 sensitive (i. e., more apt to shrink or produce artifact) 

 to the action of fixatives than at any other time; it is 

 not quite so sensitive after the spindle is fully formed; 

 during the anaphase it grows less and less so. Pollen- 

 mother-cells are usually quite sensitive just after division 

 into tetrads. Resting stages of the cell are the least sen- 

 sitive of all, and the degree of sensitiveness seems to be 

 in inverse ratio to the amount of protoplasm in the cell. 

 The nucleus is always far more resistant than the cytoplasm. 



At every step in the processes subsequent to fixing, the 

 material was subjected to careful examination in order to 

 guard against artifact. These observations showed that 

 the points requiring most care are the washing out of the 

 fixative and the infiltration with oil. Either of these pro- 

 cesses if too prolonged will frequently affect the structure 

 of the cytoplasm; they should therefore be carefully 

 controlled. 



The treatment of the material after fixing was as follows: 



