ix THE GLOBULINS 367 



as has serum- globulin, but it is completely precipitated by acids. Its 

 iodine-content is remarkable. The human thyreo-globulin has the 

 following percentage composition : 



^51'81 "6' 88 ^15'49 ^1'87 Vs4 ^23' 57- 



The composition of the thyreo-globulin of other animals is nearly 

 the same as that of man. Its coagulation-temperature is 65. 



It is not a salt, but an iodo-albumin. On it depends the physio- 

 logically and pharmacologically specific activity of the thyroid gland. 

 It forms the chief constituent of the colloid, and is enormously in- 

 creased in goitre. The iodine-percentage varies according to the age 

 of the person and also under other conditions, and does not seem to 

 play a great part in the function of the gland. 



3. Crystallin 



This expression was first used by Berzelius for the albuminous 

 substances of the crystalline lens. Laptschinsky l showed that it was 

 composed of a globulin (or vitellin) and an albumin. Subsequently it 

 was investigated by Morner, 2 who distinguishes : 



1. The a-crystallin. It gives the same reactions as does serum- 

 globulin, but it is not precipitated by sodium chloride, and only by 

 high concentrations of ammonium sulphate. It also differs from 

 globulin in not being precipitated on being diluted with water. It 

 does not give the lead-sulphide reaction. 



D = -46-9. 



Its coagulation-temperature is 72. 



It occurs principally in the outer layers of the lens. 



2. The /2-crystallin. It is only with difficulty precipitated by 

 acetic acid and carbonic acid, but otherwise it gives the ordinary 

 globulin reactions. 



a D = -43-3. 



Its coagulation-temperature is 63. 



It occurs principally in the inner, firmer portions of the lens. 



4. Egg-Globulin 



The long-known egg-globulin has been investigated and analysed 

 most recently by Langstein, 3 who found amongst the dissociation- 



1 M. Laptschinsky, P/tilgers Arch. f. d. ges. Physiol. 13. 631 (1876). 



2 C. T. Morner, Zeitschr. /. physiol. Cliem. 18. 61 (1893). 



3 L. Laugstein, Hofmeister's Beitrage, 1. 83 (1901). 



