CYTOCHROME 



27 



bands are clearly seen, press on the cover glass so as gradually to 

 decrease the thickness of the layer of muscle. In proportion as the 

 layer becomes thinner the bands will disappear, one by one, in the 

 reverse order to that in which they appeared. At last only the most 

 prominent band in the cytochrome spectrum remains visible. 



The four bands of the cytochrome from bee's muscle have their 

 positions of maximum density placed as follows : 



band a = 6046 a.u., 6 = 5665 a.u., c = 5502 a.tj., d = 5210 a.u. 



The facts described above illustrate the ease with which mistakes 

 may be made in the quest of such spectra. A spectrum in some new 

 object might be seen with one, two, three or four bands. Such might 

 be described as different spectra and attributed to the presence of 

 different materials but these apparently diverse spectra would be 

 caused merely by different dilutions of a single substance having 

 a spectrum with four bands of different densities. It may be said 



Fig. 4. Spectrum of absorption of cytochrome in the thoracic muscles of the bee. 



at once that in no material in which the c-band has been seen have 

 the other three bands failed to appear when the material has been 

 concentrated, or rather the layer of material thickened to the 

 adequate extent; and as the c-band of cytochrome is one of great 

 intensity it soon came to be recognised by Keilin as a sort of label 

 for the whole spectrum, a fact which greatly facilitated his researches 

 into the widespread distribation of this material. 



So far we have considered bee's muscle because in the bee we have 

 a creature which is uncomplicated by the presence of haemoglobin. 

 The same is true of many other forms of animal life. 



The following list, showing the wide distribution of cytochrome, is 

 given by Keilin : 



TuRBELLARiA. Dendrocda lactea. 



OLiGOCHiETES. Allolobophora chlorotica, Helodrilus caliginosus. 



Nematodes. Ascaris megalocephala, Ascaris suis. 



Molluscs. Limnea peregra, L. stagnalis, Helix nemoralis, H. aspersa. 



Crustacea. Oniscus sp., Asellus aquaticus. Cancer pagurus. 



Myriapods. Lithobius forficatus. 



