100 ALEXANDER L. DOUNCE 



The colloid mill acts mainly by creating high shearing forces in the liquid 

 medium, and is more or less free from the effects of mechanical battering 

 such as is caused by the blades of the Waring Blendor. No doubt some me- 

 chanical effects occur however, since the flow is undoubtedly turbulent ow- 

 ing to the high speed of rotation, and some if not all of the cells must strike 

 the surfaces of the cones with considerable force. 



One great advantage of the colloid mill is that a large quantity of homog- 

 enate may be very rapidly processed, since a few minutes usually suffice to 

 run the material through the mill once, and two or at the most three pas- 

 sages through the mill suffice to give practically complete cell breakdown 

 under favorable conditions. 



Another advantage of the colloid mill is that it has a less pronounced 

 tendency to disintegrate the nuclei than has the Waring Blendor. More- 

 over it will rupture whole cells more efficiently than does the Waring Blen- 

 dor, so that it is possible to obtain preparations of nuclei in cases where the 

 cells are so resistant that the Waring Blendor will not break them or will 

 do so only with simultaneous breaking of the nuclei. 



The colloid mill is however, not without several disadvantages. In the 

 first place, some sort of preliminary homogenization has to be carried out 

 in order to get the material into a sufficiently liquid state to be run through 

 the mill. As a rule a very short treatment in the Waring Blendor is satis- 

 factory for this purpose (about 1 minute, with a rather low speed). When 

 this procedure is followed, it is best to strain the material to remove fiber 

 before using the colloid mill, but the finest cloth (cotton flannel or bolting 

 silk) should not be used until the material has been passed through the 

 colloid mill. 



Another disadvantage of the colloid mill is that, like the Waring Blendor, 

 it disrupts mitochondria. As already has been noted, this is not desirable if 

 the nuclei are to be used for enzyme studies. 



Still another disadvantage is that the resistance of the nuclei to disinte- 

 gration must be increased by adding calcium chloride or lowering the pH 

 as is done when the Waring Blendor is used. Such procedures also as a rule 

 increase to some extent the resistance of the whole cells to breakdown, as 

 has already been mentioned. 



In spite of the disadvantages just cited, the colloid mill is very useful in 

 preparing large quantities of cell nuclei from organs such as liver or pan- 

 creas, and this is of considerable importance when it is desired, for instance, 

 to proceed further to isolate nucleoli from the isolated nuclei, or to prepare 

 relatively large amounts of lipid, protein, or nucleic acid from nuclei. A 

 cheaper type of hand-operated colloid mill has been used by Denues^* in 

 the isolation of chromosomes. 



16 A. R. T. Denues, Exptl. Cell Research 3, 388 (1952). 



