162 HANDBOOK OF PHYSIOLOGY. 



oughly washed out into that compartment, and the blood and water are 

 mixed with a wire. Water is then added until the blood compartment 

 is quite full. The other compartment is filled with water. Light is 

 then reflected by the mirror, S, so as to illuminate both compartments. 

 By moving K by means of the milled head, T* a position of K may be 

 found corresponding to the exact intensity of the light passing through 

 the two compartments; this is read off at 3/on the scale P, the division 

 of which corresponds to standard strengths of solutions of haemoglobin. 

 Distribution of Haemoglobin. Haemoglobin occurs not only in the 

 red blood-cells of all vertebrata (except amphioxus and leptocephalus 

 whose blood-cells are all colorless,) but also in similar cells in many 

 Worms; moreover, it is found diffused in the vascular fluid of some 

 other worms and certain Crustacea; it also occurs in all the striated mus- 

 cles of Mammals and Birds. It is generally absent from un striated 

 muscle except that of the rectum. It has also been found in Mollusca 

 in certain muscles which are specially active, viz., those which work the 

 rasp-like tongue. 



Derivatives of Haemoglobin. 



Haematin. By the action of heat, or of acids or alkalies in the 

 presence of oxygen, haemoglobin can be split up into a substance called 

 Hep-matin, which contains all the iron of the haemoglobin from which it 

 was derived, and a proteid residue. Of .the latter it is impossible to say 

 more than that it probably consists of one or more bodies of the globu- 

 lin class. If there be no oxygen present, instead of haematin a body 

 called haemochromogen is produced, which, however, will speedily 

 undergo oxidation into haematin. 



Hagmatin is a dark brownish or black non-crystallizable substance of 

 metallic lustre. Its percentage composition is C. 64.30; H. 5.50; N. 

 9.06; Fe. 8.82; 0. 12.32; which gives the formula C 68 , H 70 , N s , Fe 2 , 

 do (Hoppe-Seyler). It is insoluble in water, alcohol, and ether; solu- 

 ble in the caustic alkalies; soluble with difficulty in hot alcohol to which 

 is added sulphuric acid. The iron may be removed from hsematin by 

 heating it with fuming hydrochloric acid to 160 C. (320 F.), and a 

 new body, haematoporphyrin, the so-called iron-free haamatin, is pro- 

 duced. Haematoporphyrin (0 68 , H 74 , N 8 , Oi 2 , Hoppe-Seyler) may also be 

 obtained by adding blood to strong sulphuric acid, and if necessary 

 filtering the fluid through asbestos. It forms a fine crimson solution, 

 which has a distinct spectrum, viz., a dark band just beyond D, and a 

 second all but midway D arid E. It may be precipitated from its acid 

 solution by adding water or by neutralization, and when redissolved 

 in alkalies presents four bands, a pale band between c and D, a second 

 between D and E, nearer D, another nearer E, and a fourth occupying 

 the chief part of the space between b and F. 



