104 CARNEGIE INSTITUTION OF WASHINGTON. 



ment of our knowledge of cell structure. In coming to us, Dr. Lewis 

 will be freed from teaching and will thus be enabled to devote his entire 

 time to the continuation of his research work. 



CYTOLOGY. 



Although the structure and function of mitochondria constitute a 

 relatively new field of research, a great many investigations have 

 already accumulated, and it is now found necessary to attempt to 

 harmonize some of the results. Two papers have been published from 

 this Department during the past year which review the present status 

 of the problem and tend to reconcile divergent theories. Mention was 

 made in my last report of one by Professor E. V. Cowdry, which 

 appeared too late to be reported at length at that time. In view of the 

 importance of this contribution, some account of it should be given here. 



The consideration of mitochondria is inseparable from the fundamen- 

 tal problem of the structure of living protoplasm, and Dr. Cowdry pre- 

 sents this whole matter in a comprehensive way. In connection with 

 his introductory account of the development of our present knowledge 

 of mitochondria, he gives most useful summaries of the varieties of 

 tissue-cells and of the different animal and plant forms in which they 

 have been described, together with the names of the investigators in 

 each instance. The wide distribution of the mitochondria, as seen from 

 his tables, is amazing. They are found in all tissues, from man to the 

 lowest protozoon, and from angiosperms to the fungi, though their 

 existence is doubtful in the myxomycetes, schizomycetes, and most of 

 the algse. They are as characteristic of the cytoplasm as chromatin 

 is of the nucleus. They are found in all stages of life — in the egg and 

 in all tissues of the developing embryo and of the adult. In the part 

 devoted to technique, morphology, and distribution. Dr. Cowdry 

 makes use of much unpublished data of his own, as he does more or 

 less throughout the whole contribution. In connection with the varia- 

 tions in the amount of the mitochondria, he points out that their pres- 

 ence in large numbers is associated with intense protoplasmic activity. 

 They are especially numerous in the active stages of cell life and dimin- 

 ish with senility, in both plants and animals. There is a sharp increase 

 with regenerative activity and in compensatory hypertrophy. In the 

 second place, there is a distinct reciprocal relationship between the 

 amount of mitochondria and the amount of fat, which suggests some 

 connection between the mitochondria and oxidation. Their abundance 

 in the active stages of the life of the cell, when protoplasmic respiration 

 is rapid, points to the same conclusion. In the section dealing with the 

 chemical constitution of mitochondria a complete account is given of 

 the author's observations on the reaction of these structures to Janus 

 green and other vital stains. As regards their physiology, it is clear, 

 from Dr. Cowdry's own experience and that of others working with 



