82 THE BODY AT WORK 



doubtedly the source of bilirubin, and general considerations 

 lead to the conclusion that it is split into protein, iron, and 

 iron-free pigment in the spleen ; but the details of this process 

 have never been checked by chemical analysis. Neither bile- 

 pigment nor an iron compound can be detected in the blood 

 of the splenic vein. The only evidence of the setting free of 

 iron in the spleen is to be found in the fact that the spleen 

 yields on analysis an exceptionally large quantity of this metal 

 (the liver also yields iron), and that the quantity is greatest 

 when red corpuscles are being rapidly destroyed. 



As a rule, it is very difficult to detect leucocytes in the act 

 of eating red corpuscles ; but under various circumstances 

 their activity in this respect may be stimulated to such a 

 degree as to show them, in a microscopic preparation, busily 

 engaged in this operation. The writer had the good fortune to 

 prepare a spleen which proved to be peculiarly suitable for this 

 observation (Fig. 5). His method was an example of the way 

 in which a physiological experiment ought not to be conducted. 

 Having placed a cannula in the aorta of a rabbit, just killed 

 with chloroform, he was proceeding to wash the blood out of 

 its bloodvessels with a stream of warm normal saline solution, 

 when the bottle from which the salt-solution was flowing over- 

 turned. Fearing lest an air-bubble should enter the cannula, 

 he hastily poured warm water into the pressure bottle, and 

 threw in some salt, in the hope that it would make a solution 

 of about 0-9 per cent. The salt-solution was allowed to run 

 through the bloodvessel for rather more than an hour. When 

 sections of the spleen were cut, after suitable hardening, 

 every section was found to be packed with leucocytes gorged 

 with red corpuscles. Some of the corpuscles had just been 

 ingested ; from others the haemoglobin had already been 

 removed. It may be that, for some unknown reason, the 

 destruction of red corpuscles was occurring in this particular 

 rabbit with unusual rapidity at the time when it was killed ; 

 but it seems more probable that the animal's leucocytes were 

 provoked to excessive activity by changes in the red cor- 

 puscles brought about by salt-solution which was either more 

 or less than " tonic." As a score of attempts to reproduce the 

 experiment, with solutions of different strengths, have failed, 

 it is impossible to be sure that this is a valid explanation. 



