202 W. D. HALLIBURTON. 



cyanide of potassium are added to a litre of concentrated solu- 

 tion of haemoglobin. A quarter of a litre of alcohol is added, 

 and the mixture frozen. After one or two days' exposure to 

 this low temperature abundant crystals of a brown colour, 

 which give the absorption spectrum of methsemoglobin, are 

 deposited. They were obtained in this way from the hsemo- 

 globin of the dog, pig, and horse, and their form is the same 

 as that of the oxyhsernoglobin crystals of the same animals, 

 i. e. rhombic prisms. Dr. Gamgee 1 had prepared these crystals 

 from dog's blood many years previously, but their true nature 

 was not at that time recognised. His method was much the 

 same as Hiifner's, the chief difference being that the nitrite 

 of potassium or amyl was employed instead of ferricyanide of 

 potassium. 



Jaderholm 2 has also obtained these crystals from dog's 

 blood by the ferricyanide method, and confirms Hiifner's 

 statement that they are rhombic prisms. He also figures 

 some crystals of methsemoglobin obtained by Profossor Ham- 

 marsten from the horse by the same method, which were regular 

 six-sided plates, and showed no double refraction if lying flat ; 

 they therefore presumably belonged to the hexagonal system, 

 and were more insoluble in water than the crystals of dogs' 

 methsemoglobin. I can find no previous reference to the 

 methsemoglobin crystals of rodent animals. 



Hiifner's ferricyanide method is applicable when one wishes 

 to obtain large quantities of the crystals for analysis. I now 

 wish to describe a much simpler method of obtaining these 

 crystals for purposes of microscopic observation. I have tried 

 this method with the blood of the ox, dog, cat, rabbit, rat, 

 guinea-pig, and squirrel, but only successfully in the three last- 

 named animals. In other words, methaernoglobin crystals are 

 obtained with ease from the same animals as yield, oxyhemo- 

 globin crystals with readiness. 



The method consists in taking a few cubic centimetres of 



1 A. Gamgee, "The Action of Nitrites on Blood," 'Pliilos. Trans.,' 1868, 

 p. 589, et, seq. 



2 ' Zeitschrift fur Biologie,' Bd. xx, p. 419. 



