l8 PLANT DISEASE 



CHAPTER II 



CHLOROPHYLL AND HAEMOGLOBIN 



NATURALLY normal blood must contain the 

 constituents of the whole body, as it is by 

 this means that the wear and tear of the body 

 is made good. For instance, the blood must 

 convey to the nails, hair, teeth, etc., the con- 

 stituents that go to build them up, and if it 

 is wanting in these constituents, we see the 

 teeth decaying, the hair falling out for want 

 of nourishment, the nails becoming thin and 

 weak like those of consumptives. Beyond the 

 constituents that go to build up the parts 

 there is the constituent which may be said to 

 be the very essence of animal life, namely, 

 haemoglobin. The functions of this con- 

 stituent of the blood are so all-pervading that 

 one can scarcely go too fully into the subject. 

 In the first place, it is admitted that arterial 

 blood, that is, the blood as it leaves the lungs, 



