86 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



tainly the variations are not so great as are those between the mitochondria in 

 different varieties of cells. Fundamentally the problem is the same, because the 

 variations between different types of cells arise throughout the course of histo- 

 genesis. 



In phylogenesis also we have to deal with certain variations in the constitution 

 of mitochondria, but here it is greater. The technique which we use has to be 

 specially adapted to almost every form that we study. There is undoubtedly 

 some difference in the mitochondria. It is not all a question of their surround- 

 ings. A case in point is that of Planaria, in which I have attempted, again and 

 again, to identify the structures which Korotneff (1909, p. 1010) has described 

 under the heading of "Mitochondria." I have found that they are satisfactorily 

 fixed in mixtures like acetic sublimate, which destroy mitochondria in mammalian 

 tissues; and, conversely, that the methods which I have been accustomed to use 

 for higher forms fail completely. This experience has impressed upon me the 

 danger wliich lies in arguments that since the mitochondria do something in one 

 type of cell thej' must necessarily do it also in another. 



N. H. Cowdry (1917, p. 217) has made the first detailed comparison of the 

 microchemical reactions of plant and animal mitochondria. His general conclu- 

 sion (p. 225) is as follows: 



"We have every reason to suppose that their chemical composition is much the same 

 in both plants and animals, but here our knowledge is for the most part supposition and 

 inference, since direct chemical analyses are obviously out of the question. Their com- 

 position, as indicated by solubility with respect to acetic acid, heat, and other reagents, 

 is certainly subject to similar variations in both." 



We know very little of variations in the constitution of mitochondria in differ- 

 ent physiological conditions, though they probably occur. The only reference 

 known to me of work along this line is Policard's (1912c?, p. 229) on the tempera- 

 ture solubihty of mitochondria in kidney-cells, in which he makes the unqualified 

 statement that the temperature solubihty varies with the state of physiological 

 activity. This should be confirmed. 



In conclusion, we may say that slight variations do occur in the chemical con- 

 stitution of mitochondria in different varieties of cells, in the course of histogenesis 

 and phylogenesis, and in different physiological states, though we do not know 

 their nature or extent. They are the exception rather than the rule, but they 

 must nevertheless be kept in mind when we venture to argue by analogy. 



REACTION TO JANUS GREEN. 



Michaehs (1899, p. 565), while making a detailed study of the beha\dor and 

 chemical nature of vital dyes, found that janus green stained certain filaments in 

 gland-cells specifically. The janus green was obtained from the Farbwerke Hoechst 

 Company. He called it diethylsafraninazodimethylanilin, and gave it the formula 

 shown in figure A. He was careful to emphasize that a slight alteration in the 

 composition of the janus green alters the specificity of the stain, for he found 



