u THE PIGMENTS OF ORGANISMS 29 



the contained iron, it possesses the power of forming 

 a loose combination with oxygen, and so of acting as 

 a respiratory pigment. Of its origin little is known, 

 but there seems to be some reason to believe that in 

 development it arises from the chromatin of the 

 nucleus. In a recent paper on iron-compounds in 

 animal and vegetable cells by Dr. Macallum, the 

 author puts forward the theory that the chromatin, 

 that part of the nucleus which readily takes up stains, 

 is an iron-holding nucleo-albumen. This chromatin 

 has the power of fixing free oxygen, and the forma- 

 tion of haemoglobin results in the conversion of the 

 nuclein into the pigment hsematin ; the substance re- 

 taining its primitive power of forming a combination 

 with oxygen. Further, Dr. Macallum regards the 

 diminished amount of hsemoglobin in the blood in 

 anaemia not as the prime cause of the disease, but as 

 one of the results of the deficiency of iron-containing 

 compounds in the nuclear chromatin ; this deficiency 

 being the prime cause of the various symptoms of the 

 disease. The distinction may seem unimportant, 

 but it is not so in reality ; for if Macallum's view be 

 correct, it carries us one point further. Anaemia is 

 recognised in our own species by the pallor of the 

 lips and skin produced by the diminution in the 

 number of red blood corpuscles ; it is therefore 

 natural to conclude that the disease is caused by 

 the insufficient amount of haemoglobin present. If, 

 however, it is proved that this absence of haemoglobin 

 is itself merely a consequence of something deeper 

 which affects the whole organism, we are at least a 

 little nearer the problem of the primary meaning of 

 haemoglobin. 



