212 VETEEINAEY PHYSIOLOGY 



one filled with a 1 per cent, solution of normal blood 

 saturated with CO, and another in which 20 cmm. of blood 

 to oe examined, measured in a pipette, is placed in water, 

 mixed with coal gas to saturate with CO, and then diluted 

 till it has the same tint as the standard tube. The per- 

 centage of haemoglobin in terms of the normal is indicated by 

 the mark on the tube at which the fluid stands. (Chemical 

 Physiology.) 



Methsemoglobin. Haemoglobin forms another compound 

 with oxygen methaemoglobin. The amount of oxygen is 

 the same, but methsemoglobin must be acted on by the 

 strongest reducing agents before it will part with its oxygen. 

 When, therefore, this pigment is formed in the body, the 

 tissues die from want of oxygen. It may be produced by the 

 action of various substances on oxyhaemoglobin. Among 

 these are ferricyanides, nitrites, and permanganates. It 

 crystallises in the same form as oxyhaemoglobin, but has a 

 chocolate brown colour. Its spectrum is also different from 

 haemoglobin or oxyhsemoglobin, showing a narrow sharp band 

 in the red part of the spectrum, with two or more bands in 

 other parts according to the reaction of the solution in which 

 it is dissolved (fig. 103). It is of importance since it occurs in 

 the urine in some pathological conditions. In all probability 



/ 



the molecule of oxy haemoglobin has the formula Hb/ | , 



X 



o 



while in methaemoglobin the atoms are arranged Hb 



Haemoglobin also combines with certain other gases. Among 

 these is Carbon monoxide. For this gas haemoglobin has a 

 greater affinity than for oxygen, so that when carbon monoxide 

 haemoglobin is once formed in the body, the blood has little 

 power of taking up oxygen, and the animal dies. This gas is 

 evolved freely in the fumes from burning charcoal, is present 

 in coal gas, and is found in the air of coal mines after 

 explosions. Carbon monoxide haemoglobin forms crystals like 

 oxyhaemoglobin, and has a bright pinkish red colour, without 

 the yellow tinge of oxyhaemoglobin. Since after death it does 

 not give up its carbon monoxide and become changed to purple 



