CYTOCHROME _^ - -^ 37 



its development. The adult insect, however, does not contain the maximum amount 

 of pigment immediately on hatching. This is reached during adult life. 



2, The claim of cytochrome to be a peroxidase is stated by Keilin 

 as follows: 



Cytochrome and its derivatives have the properties of a thermostable peroxidase. 

 All the tissues when cytochrome is present and can be seen spectroscopically, give 

 a good reaction with benzidine, and with guaiacum and hydrogen peroxide. The 

 tissues of invertebrates where the pigment is very meagre give a very weak reaction or 

 none at all. In a single individual, Dytiscus for example, the brown muscles, which 

 are rich in cytochrome, give a strong positive peroxidase reaction, while the white 

 muscles, which are very poor in cytochrome, give hardly any reaction. 



3. No discussion of the significance of cytochrome can close with- 

 out some reference to a problem which has fascinated biologists now 

 for a quarter of a century, namely, the relation of the group of pigments 

 in the animal kingdom, which finds its highest development in 

 haemoglobin, to that without which only the humblest forms of 

 vegetable life exist, namely, chlorophyll. The fact of the pyrrol group- 

 ings existing in each has prompted the use of the word "Suggestive" 

 with the largest possible capital S : hitherto, however, the suggestions 

 have failed to yield the fruit of any biological relation between the 

 two sets of pigments. Verne (5) has gone so far as to suppose that the 

 hsematin pigments of animal life are derived from the chlorophyll 

 contained in the ingredients of the vegetable food. Now the facts 

 must be orientated afresh : in more primitive forms of life than those 

 in which either haemoglobin or chlorophyll exist, there may be found 

 the tetrapyrrol grouping in hsematin and cytochrome. Yeast and 

 bacteria for instance fed on media entirely free from chlorophyll 

 exhibit the spectral bands of cytochrome and haematin. If chemical 

 relationship and phylogeny have any thing to do with one another 

 it is more probable that chlorophyll has been derived by the living 

 organism from hsematin than haematin from chlorophyll. 



Is this " Suggestive " ? The yellow portions of the leaf of Euonymus 

 contain cytochrome, the green ones chlorophyll. 



REFERENCES 



(1) Keilin. Proe. Roy. Soc. B. xcviir. 312. 1925. 



(2) MacMunn. Phil. Trans. Roy. Soc. CLXXvn. 267. 1886. 



(3) Keilin. Proc. Roy. Soc. B. c. 129. 1926. 



(4) Keilin. C. R. de la Soc. de Biol. Paris. Reunion pl^niere, xcvn. 39. 1927. 



(5) Verne. "Les Pigments dans I'organisme animal." ^?ici/cfop. /Scien/. Doin, 1926. 



