On Absorption. 173 



solution of iron, not the slightest reaction took place ; so 

 also when applying a solution of the ferrocyanide to the part 

 beneath the skin, where the iron had been injected, no 

 reaction occurred. In none of the tissues were either 

 found in a free state. The alimentary canal, which had 

 contained iron a few hours before in such abundance, now 

 gave signs of none. 



From this experiment we infer, that in twenty-three hours 

 the ii^on had either entered into very stable combinations in 

 the body, or had passed out of the body in the urine in equal 

 stable combination ; or uniting with the ferrocyanide, was 

 actually present in the tissues and fluids in the form of the 

 minute * blue crystals before spoken of as seen in the blood 

 and chyle. 



It is not to be supposed that these salts are absent from a 

 tissue because they do not answer to ordinary chemical tests. 

 The spectroscope must be used. Here is an illustration of its 

 use : Mr. Bowman, the distinguished occulist and physiolo- 

 gist, had a patient with double soft cataract ; she took twenty 

 grains of carbonate of lithium, seven hours after which one 

 e^^e was operated on, and the lens removed. The 

 minutest portion showed abundance of chloride of lithium 

 in the spectrum. Seven days having elapsed, the other lens 

 was removed, but not a trace of the salt could be detected. 

 This was a paii: of a series of experiments recently made by 

 my former teacher, Dr. Bence Jones, to whom I am much 

 indebted for instruction in what may be termed clinical 

 chemistry. 



Experiment 2. — One and a-half ounce of solution of per- 

 cliloride of iron were injected into the peritoneal cavity, and 

 one and a-half ounce of solution of ferrocyanide of potas- 

 sium beneath the skin of the back of a dog. 



At intervals during the succeeding twenty-four hours, I 

 frequently examined the blood for free iron and ferrocyanide, 

 but found none ; but beneath the microscope crystals on 

 evaporation, as in the blood of the cock. 



Twenty-six hours after the injections a large quantity of 

 urine was passed, to some of which, when a drop or two of 

 perchloride of iron was added, a large quantity of prussian 

 blue was formed. No trace of fr-ee fron. A drop of the urine 

 evaporated on a slide showed beneath the microscope an 



* When I use the word '• minute," I mean something sensibly much 

 smaller than a human red blood-corpuscle. 



