1 68 RESPIRATION 



kind or another within the corpuscles. Figure 53 shows the per- 

 centage conversion to methaemoglobin in the blood of a rabbit at 

 intervals after a non-poisonous dose of sodium nitrite. It will be 

 seen that after four hours the blood had completely recovered. 



The action of methaernoglobin- forming poisons is rendered 

 evident at once by the marked cyanosis which they produce. The 

 methaemoglobin has a dark color, and the arterial blood becomes 

 therefore of a chocolate or coffee color. This form of cyanosis may 

 become very marked indeed without serious real symptoms of an- 

 oxaemia being present. Thus in acute poisoning by dinitrobenzol 

 (an ingredient of certain explosives) a man may become very blue 

 in the face and yet be going about as usual, although he presents 

 a most alarming appearance. 



Many of the poisons which produce methaemoglobin cause, in 

 addition, radical decomposition in the haemoglobin, and even 

 breaking up of the red corpuscles. This is, for instance, the case, 

 to a large extent, with dinitrobenzol, so that there are other colored 

 decomposition products present as well as methaemoglobin; and 

 for the present it is not possible to specify their nature. Their pres- 

 ence, or that of methaemoglobin, can, however, be detected at once 

 on diluting a drop of the blood till the color begins to become 

 yellowish, then saturating with coal gas or CO, and comparing 

 the tint with that of normal blood diluted to a corresponding ex- 

 tent and similarly saturated. If any colored decomposition prod- 

 ucts are present the normal blood solution will be pinker, as the 

 CO does not combine to give a pink color with these foreign 

 substances. 



When a poison causes solution of the red corpuscles (haemo- 

 lysis), or decomposes the haemoglobin beyond the methaemo- 

 globin stage, the haemoglobin is lost to the body, and "anaemia" 

 is one result of this, as well as jaundice. Thus chronic poisoning 

 by dinitrobenzol and similarly acting substances causes very seri- 

 ous anaemia. This also results from chronic poisoning by arsenu- 

 retted hydrogen, which has the peculiar action of injuring the 

 walls of the red corpuscles and so causing haemolysis, with re- 

 sulting haemoglobinuria, jaundice, and often nephritis. We are 

 thus brought to the consideration of the anoxaemia caused by 

 anaemia, the word "anaemia" being taken to mean simply a 

 diminution in the percentage of haemoglobin in a given volume 

 of blood, whether the blood volume itself is diminished, or normal, 

 or increased. As a matter of fact the blood volume is usually much 



