CHROMATOI.YSIS. 75 



etc.). Unicellular organisms such as amebae, infusoria, and many low 

 forms of vegetable life make also good material for this purpose. 



Protoplasmic currents are best seen in the tactile hairs of the net- 

 tle. Should fresh animal cells be desired, amebae can occasionally be 

 found in muddy or marshy water. The same phenomena may be ob- 

 served in the leucocytes of the frog or, better still, in the blood of the 

 crab. 



In order to make a detailed study of the minute relationship 

 of the different cellular structures, it is necessary to fix the cells ; the 

 same is true of nuclear division and cell proliferation. Although this 

 process has been observed in living cells, it was not until it had been 

 thoroughly worked out in preserved preparations. The best results in the 

 study of the cell are obtained by methods that will be subsequently 

 described. Fresh tissues are absolutely essential. 



According to Hammer, mitosis in man does not cease immediately 

 after death. The nuclei suffer chromatolytic destruction, and the achro- 

 matic spindle is the last element to disappear. 



Flemming's solution here deserves first mention as a fixative. The 

 tissues are imbedded, sectioned, and stained with safranin. An equally 

 good fixative is Hermann's solution, which may be combined with a sub- 

 sequent treatment with pyroligneous acid. Rabl fixes with a o. i-o. 12 '-/< 

 solution of chlorid of platinum, washes with water, passes into gradually 

 stronger alcohols, then stains with Delafield's hematoxylin, and finally 

 examines the preparation in methyl alcohol. 



Mitoses can also be seen by fixing in corrosive sublimate, 

 picric acid, chromic acid, etc., and staining in bulk with hematoxylin 

 or carmin, although perhaps not so well as by the preceding method. 

 The objects to be examined are best when obtained from young and grow- 

 ing animals, especially those possessing large cells. Above all are to be 

 recommended the larvae of amphibia, like the frog, triton, and sala- 

 mander. If examination by means of sections be undesirable, thin 

 structures should be procured, such as the mesentery, alveoli of the lungs, 

 epithelium of the pharynx, urinary bladder, etc. These have the advan- 

 tage of enabling one to observe the whole cell instead of parts or frag- 

 ments of cellular structures. In sections of a larva that has been fixed in 

 toto, mitotic figures can be seen in almost all the organs, and are particu- 

 larly numerous in the epithelium of the epidermis, gills, central canal of 

 the brain and spinal cord, etc. Other organs, such as the blood, liver, 

 and muscle, also show mitoses. 



Certain vegetable cells are peculiarly adapted to the study of 

 mitosis, as, for instance, those in the ends of young roots of the onion. 

 The onion should be placed in a hyacinth glass filled with water and kept 

 in a warm place. After two or three days numbers of small roots will 

 be found to have developed. Beginning at the points, pieces 5 milli- 

 meters in length are cut, which are treated in the same manner as animal 

 tissues. These are then cut, either transversely or longitudinally, into 

 very thin sections (not over 5 // in thickness). In one plane, polar views 

 of the mitoses are obtained ; in the other, lateral views. 



The methods used for demonstrating the remaining parts of the 

 cell and its nucleus (except the chromatin) are, as a rule, more compli- 

 cated, and. consequently less reliable. In order to see the centrosome, 

 the spindle fibrils, the linin threads, and the polar rays, one of the 



