64 



DISCOVERY REPORTS 



fore in fair agreement considering the indirect methods used for analysis. There is no 

 doubt that the usually accepted trihydrate formula for the tetragonal calcium oxalate 

 is incorrect, and there is at least a strong probability that the formula should be 

 CaQO^.aH^O. 



Table I. Chemical analyses of renal calcium oxalate crystals, sp. gr. 1-99 



Table II 



It is interesting to note that this conclusion is in agreement with the results of the 

 earliest workers (T. Graham, 1838). No completely satisfactory analysis of the salt, 

 however, has yet been published. A. Frey (1925), who claims to have produced artificial 

 crystals h mm. across, records a figure for the water content only and deduces the 

 formula CaC204.3H20. It is not, however, obvious with what measure of success he 

 separated the tetragonal salt from associated products of crystallization. His optical 

 data are also at variance with mine; he gives to 1-552, e 1*583, presumably measured on 

 the artificial salt and it is significant that these values are close to those that would be 

 observed for a crystal of whewellite, CaCaOj . HoO, lying on the face x (on), viz. y' 1-551, 

 a' 1-592. In view of this disagreement in refractive index measurements some of his 

 identifications of the tetragonal cr}^stals in plants must be accepted with reserve. 



Many references to the presence of calcium oxalate in the waste products of plants 

 and animals also record the size of the " envelope " crystals. C. Schmidt (1846) studied 

 their formation in yeast covered by beer for many days. He also detected them in the 

 gall of rabbit, dog and pike. The crystals usually measured o-oi x 0-005 mm. and were 

 never greater than 0-03 mm. across. Frey has observed crystals definitely of the tetra- 

 gonal form in Begonia species of size 0-023 ^ 0-013 "^^n- They are also a usual con- 

 stituent of human urine especially during the summer months. A sample of urine of 

 patients suffering from oxaluria kindly sent to me by Mr L, W. Proger, Pathological 

 Curator of the Royal College of Surgeons, shows many "envelope" crystals 0-02- 

 0-025 I"""''- across, refractive index at = 1-52. Golding Bird (1843) made a microscopic 

 and chemical study of "envelope" crystals in human urine and was the first worker to 



