MITOCHONDRIA IN PLANT AND ANIMAL CELLS. 2 07 



those in fixed tissues. The general tendency of fixatives is to 

 shrink them and to make them uniformly smaller than they 

 really are in the living condition. This tendency is very slight, 

 almost negligible, in the case of the best fixatives. On the other 

 hand, acetic acid, and possibly also formalin in very low con- 

 centrations-, have a marked swelling effect. 



It must be admitted that variations sometimes do occur in 

 the mitochondria in our preparations, particularly in the pea, 

 for which no reasonable explanation can be advanced on the 

 basis of the technique. They may result from rhythmical 

 variations in the activity of the cells which we have reason to 

 believe occur, just like periodicity in cell division, many cells 

 dividing almost synchronously (Kellicott, '04, p. 531) but they 

 cannot be wholly explained in this way. They may result also 

 from the conditions under which the radicle is growing, upon 

 whether it is submerged or exposed to the air; but I find that 

 radicles grown under exactly the same conditions occasionally 

 show mitochondrial variations which are very perplexing. 



Evidently the experimental error is something which we must 

 have considerable respect for, but which can be controlled if the 

 proper precautions are taken. Its identity in plant and animal 

 tissues is another indication of the similarity of the mitochondria 

 in the two. 



There is another factor, often very confusing, which we have 

 to bear in mind, namely that of the production of coagula in the 

 homogeneous ground substance. They are formed in the proto- 

 plasm of the pea radicle by exposure for about 30 minutes to a 

 temperature of 48 C. or higher and also by fixatives containing 

 acetic acid, chromic acid, corrosive sublimate or alcohol. Iron 

 hematoxylin, when imperfectly differentiated with iron alum 

 solution, stains these coagula in the same manner as the mito- 

 chondria and in many cases no clearly marked distinction can 

 be made between them, since they both vary very much in their 

 resistance to differentiation. The formation of these coagula is 

 generally accompanied by distortion, fragmentation or destruc- 

 tion of the mitochondria. In the cells of the pancreas these 

 fixatives bring about a distinctly fibrous appearance in the nor- 

 mally homogeneous basophilic substance which is often as re- 



