30 HEMOGLOBIN 



observation, both pigments become rapidly reduced, the bands of 

 oxyhaemoglobin disappear, being replaced by faint bands of reduced 

 haemoglobin, while the bands of the reduced cytochrome rapidly 

 appear. 



Here we are faced with a phenomenon which will crop up later, 

 with regard for instance to haemochromogen and haemoglobin; and 

 just as we use the word "haemoglobin" to cover the whole range of 

 substances which possess spectra approximately, but not precisely 

 identical, so we will retain the word "cytochrome " to cover a similar 

 range of substances which have approximately the spectrum shown in 

 Fig. 4. The sorts of differences which occur are shown in Fig. 5. 



It may not have escaped the reader, especially if he be an organic 

 chemist, that such information as I have given about cytochrome has 

 all been gleaned by the inspection of living cells, and that neither 

 the name cytochrome nor the four-banded spectrum represents a 

 substance which has been isolated. I will not enter into the question 

 of how far a material which has not been isolated can be regarded 

 as satisfactory. I will at once concede to the organic chemist of the 

 purist school that such a material is less satisfactory than if it had 

 been isolated, but I must claim for those who are prepared to study 

 "life as a whole" that a man places an undue limitation on his 

 intellect if he is not prepared to look at living things as they are, 

 but will merely study the artifacts about which he can obtain more 

 precise information. Suffice it to say that the component cytochrome 

 has not been isolated, but although this is so the attempt has fur- 

 nished important information which goes some way to show where 

 cytochrome stands in relation especially to haemoglobin. 



The spectrum of cytochrome has been described as having four 

 bands, but one of these bands, d, when carefully examined with 

 a Zeiss microspectroscope is found to be in reality composed of three 

 bands which are more or less merged. The cytochrome spectrum has 

 therefore six bands which are related to one another in an interesting 

 way. We will call them, not a, b, c and d, but a, b, c, z, y and x. These 

 six bands may be seen in Fig. 4 in which the tripartite nature of the 

 band d is well shown. One remarkable property about the six bands 

 is that they appear to be related to one another in pairs. To start 

 with the consideration of a, 6 and c. These three bands are not always 

 of the same relative intensity. As has been said, c is usually much 

 the most Conspicuous and a the least so. In the wing muscles of the 

 bumble-bee (3), however, a is of unusual relative intensity; in the 



